Applied Catalysis B, Environmental (v.210, #C)
Editorial Board (IFC).
Exploring pretreatment effects in Co/SiO2 Fischer-Tropsch catalysts: Different oxidizing gases applied to oxidation-reduction process by Jian Cai; Feng Jiang; Xiaohao Liu (1-13).
Display OmittedThe influence of reduction-oxidation-reduction (ROR) pretreatment on 20% Co/SiO2 has been investigated using different oxidizing gases including water vapor and oxygen in the oxidation step. In this study, the evolution concerning the SiO2 structure and the cobalt phase and morphology is clearly elucidated at each step of reduction, oxidation and subsequent re-reduction. It is demonstrated that ROR treatment using both oxygen and water vapor decreases the average cobalt particle size. However, the catalytic performance affected in FTS is considerably different. ROR treatment in oxygen results in an increase in catalytic activity. In contrast, the water vapor applied in oxidation step obviously deactivates cobalt catalyst and enhances selectivity of methane. The resulting deactivation is ascribed to the promoted formation of irreducible cobalt silicate through the reaction between water vapor caused surface Si―OH groups and oxidized cobalt (CoO) in spite of unchanged surface area and pore structure on SiO2. The characterization data reveals that the re-dispersion of cobalt particles occurs at oxidation step rather than the re-reduction step. In addition, the results indicate that the ROR treatment reducing the cobalt particle size depends on its initial size as no re-dispersion can be observed in the case of particles smaller than about 11 nm. Furthermore, the water vapor shows more effective re-dispersion in cobalt particles compared with the use of oxygen. This study provides fundamental insights into the control of catalytic activity, product selectivity, and catalyst stability over supported cobalt catalysts by understanding the evolution of catalyst structure through ROR treatment in different chemical environment.
Keywords: Cobalt nanoparticles; Silica; Reduction-oxidation-reduction treatment; Water vapor; Oxygen;
Probing the functionality of nanostructured MnCeOx catalysts in the carbon monoxide oxidation by Francesco Arena; Roberto Di Chio; Barbara Fazio; Claudia Espro; Leone Spiccia; Alessandra Palella; Lorenzo Spadaro (14-22).
Display OmittedThe effects of cerium addition on the physico-chemical properties and CO oxidation activity of nanostructured MnCeOx catalysts (0 ≤ cCe ≤ 1) have been assessed. Irrespective of the loading, cerium hinders any significant long-range crystalline order promoting surface exposure, oxide dispersion, and reducibility of composite catalysts. Noticeable structural effects and strong oxide interaction lead to different arrangement of the active MnOx phase, explaining the peculiar reactivity scale of the studied catalysts in the CO oxidation reaction. High activity, good stability, CO2 productivity values depending on the MnOx loading, and similar activation energy values in the range of 353–533K (37–47 kJ/mol) uncover an unchanging reaction mechanism, irrespective of composition and temperature. Although some chemical effects at high Ce loading (χCe ≥ 0.5), structure-activity relationships indicate that surface MnIV centers are the active sites of bulk MnOx and composite MnCeOx catalysts.
Keywords: Nanostructured MnCeOx catalysts; Structural and electronic effects; CO oxidation; Structure-activity relationships; Active sites;
Rational design and synthesis of SnO2-encapsulated α-Fe2O3 nanocubes as a robust and stable photo-Fenton catalyst by Na Wang; Yunchen Du; Wenjie Ma; Ping Xu; Xijiang Han (23-33).
Display Omitted In situ transformation of metal-organic frameworks (MOFs) is becoming a fascinating strategy to construct porous metal oxides with excellent performance in many fields. In this work, Prussian blue (PB) nanocubes are employed as the precursor of porous Fe2O3 to fabricate SnO2-encapsulated α-Fe2O3 (Fe2O3@SnO2) nanocubes by pre-coating Sn(OH)Cl on the surface of PB nanocubes. It is very interesting to find that SnO2 shells can not only preserve the microstructure of Fe2O3 nanocubes from high-temperature treatment, but also facilitate the phase variation from metastable γ/β-phase to stable α-phase. The thickness of SnO2 shells can be controlled by manipulating the amount of stannous chloride. When Fe2O3@SnO2 nanocubes are applied as heterogeneous photo-Fenton catalysts, they will exhibit much better catalytic efficiency for the degradation of Rhodamine B (RhB) than PB-derived Fe2O3 and commercial α-Fe2O3. The characterization results reveal that Fe2O3@SnO2 nanocubes have similar catalytic mechanism to conventional α-Fe2O3, and stable microstructure and preferable crystalline phase are primarily responsible for this significant enhancement. Some influential factors, including H2O2 concentration, catalyst dosage, pH value, and reaction temperature are investigated and analyzed in details. Moreover, Fe2O3@SnO2 nanocubes can maintain their catalytic efficiency during the repeated batch experiments. We believe Fe2O3@SnO2 nanocubes can be a new kind of high-performance green heterogeneous catalyst for the degradation of organic pollutants, and this study may provide a new idea to upgrade the performance of some conventional catalysts by rational design in the future.
Keywords: Fe2O3@SnO2 nanocubes; Prussian blue; Phase transformation; RhB degradation; Photo-Fenton reaction;
Influence of preparation method on dispersion of cobalt spinel over alumina extrudates and the catalyst deN2O activity by Gabriela Grzybek; Sylwia Wójcik; Klaudia Ciura; Joanna Gryboś; Paulina Indyka; Marcin Oszajca; Paweł Stelmachowski; Stefan Witkowski; Marek Inger; Marcin Wilk; Andrzej Kotarba; Zbigniew Sojka (34-44).
Display OmittedA series of supported catalysts of the Co3O4 spinel active phase dispersed over alumina extrudates (9 × 25 mm) was prepared by several methods (incipient wetness impregnation with Co(NO3)2 and CoCl2, with glycerol-assisted impregnation with Co(NO3)2, combustion synthesis, and two variants of spray deposition with Co(NO3)2 on pristine and ammonia soaked extrudates). The catalysts were characterized by XRF, XRD, RS, UV–vis, SEM/TEM/EDX, and their catalytic deN2O activity was investigated in the temperature programmed surface reaction (TPSR) mode. The relation between the spinel active phase particle size and its radial dispersion over the alumina extrudate and the deN2O activity was revealed and quantified. For the assessment of the active phase utilization, the N2O concentration profile across the extrudates was calculated using Thiele modulus and compared with the radial distribution of the spinel. It was shown that the dispersion of spinel active phase exhibits optimal profile when the sample is obtained in the presence of the organic components of the precursor mixture (glycerol or urea). The obtained results were discussed in the context of practical implications for the development of an efficient, low-cost catalyst for the N2O abatement.
Keywords: Cobalt spinel; Alumina support; Preparation method; Active phase dispersion; N2O decomposition;
Peculiar synergetic effect of MoS2 quantum dots and graphene on Metal-Organic Frameworks for photocatalytic hydrogen evolution by Xuqiang Hao; Zhiliang Jin; Hao Yang; Gongxuan Lu; Yingpu Bi (45-56).
Co-catalyst is a critical factor to efficient water splitting for photocatalytic hydrogen evolution. A high active co-catalyst, MoS2 quantum dots (MoS2 QDs), anchored on UiO-66-NH2/G was employed as catalysts exhibited excellent photocatalytic activity toward hydrogen evolution from water splitting under visible light irradiation with Eosin Y as antenna molecule. Special enhanced synergetic effect of MoS2 quantum dots and graphene on Metal-Organic Frameworks for photocatalytic hydrogen evolution was obtained. The rate of H2 evolution reached 2.07 mmol h−1 g−1 over the EY-sensitized 5 wt% MoS2 QDs/UiO-66-NH2/G irradiated under visible light irradiation (λ ≥ 420 nm), and the apparent quantum efficiency (AQE) of 40.5% was achieved at 430 nm.Display OmittedSpecial enhanced synergetic effect of MoS2 quantum dots (MoS2 QDs) and graphene on metal-organic frameworks for photocatalytic hydrogen evolution is obtained here. The photocatalytic activity of H2 evolution reach 186.37 μmol over the EY-sensitized 5 wt% MoS2 QDs/UiO-66-NH2/G irradiated under visible light irradiation (λ ≥ 420 nm) in the first 3 h, and the apparent quantum efficiency (AQE) is 40.5% at 430 nm. The synergistic effect between MoS2 QDs and graphene together with UiO-66-NH2 is corroborated by photo-luminescence spectra, electro-chemical and photo-electro-chemical experiments. It demonstrate that the charge separation and the electrons transfer are more efficient with the aid of the MoS2 QDs and graphene. MoS2 QDs might be a potential photocatalyst for design new type of catalysts in photocatalysis proton reduction.
Keywords: MoS2 QDs; Metal-organic frameworks; Graphene; Photocatalytic hydrogen evolution;
3D interconnected hierarchically porous N-doped carbon with NH3 activation for efficient oxygen reduction reaction by Yi Wang; Hanyu Liu; Kun Wang; Shuqin Song; Panagiotis Tsiakaras (57-66).
Display OmittedIn the present work, a novel metal-free ORR electrocatalyst, with large specific surface area (2600 m2 g−1), high content of N dopants (3.12 at.%) and 3D cross-linking hierarchically porous structure (abbreviated as LHNHPC) is readily prepared by using a modified classical carbon-aerogel method with NH3 as the activating agent.Compared with benchmark Pt/C catalyst, it is found that, LHNHPC exhibits similar electrocatalytic activity towards oxygen reduction reaction (ORR), superior durability and excellent methanol tolerance in basic media. The above electrochemical properties of LHNHPC are mainly attributed to the synergistic contribution of its unique hierarchical pore structure, the rich N doping and the large surface area.It can be anticipated that the proposed two-step process could be used for mass production of metal free electrocatalysts for a wide range of electrochemical devices including fuel cells and metal-air batteries.
Keywords: Oxygen reduction reaction; Nitrogen-doped; Hierarchically porous carbon; Electrochemical performance;
Efficient Co@CoO core-shell nanocrystals as catalysts for visible-light-driven water oxidation by Zheng Wan; Qian Xu; Hui Li; Yi Zhang; Yong Ding; Jide Wang (67-76).
Display OmittedThis paper introduces the first attempt of using well organized Co@CoO core-shell nanocrystals as an alternative toward noble metal catalysts for photocatalytic water splitting reactions. In this work, four kinds of stable magnetic Co@CoO core-shell nanocrystals were fabricated through a one-pot toluene-water two-phase interfacial reaction with oleic acid as a surfactant. The size and shape of the as-prepared crystals can be carefully adjusted through dynamically coating the closely packed monolayer of coordinating ligand onto the growing crystals. It is notable that spherical pine-nut-like hierarchical assemblies of Co@CoO core-shell nanoplates exhibit excellent photocatalytic activity (the maximum value of O2 yield is over 96%). Even after the sixth run, the high catalytic activity of the recovered Co@CoO core-shell nanoplates remained.
Keywords: Co@CoO; Core-shell nanocrystals; Photocatalysis; Water oxidation; Visible-light-driven;
Novel 3DOM-SrTiO3/Ag/Ag3PO4 ternary Z-scheme photocatalysts with remarkably improved activity and durability for contaminant degradation by Chenxi Zhang; Kai Yu; Yajun Feng; Yue Chang; Ting Yang; Ying Xuan; Da Lei; Lan-Lan Lou; Shuangxi Liu (77-87).
Display OmittedThe novel visible-light-driven 3DOM-SrTiO3/Ag/Ag3PO4 ternary composites were fabricated and used as photocatalysts in the degradation of organic contaminants, including RhB, phenol, and MB. Through the XRD, SEM, TEM, DR UV–vis, XPS, PL spectroscopy, N2 sorption, and photoelectrochemical measurement, the obtained 3DOM-SrTiO3/Ag/Ag3PO4 ternary composites were well characterized. The effects of SrTiO3:Ag3PO4 molar ratio and stop-bands of 3DOM-SrTiO3 on the catalytic performance were systemically investigated. 3DOM-SrTiO3/Ag/Ag3PO4 ternary composite photocatalysts exhibited notably enhanced activity compared with single 3DOM-SrTiO3 and Ag3PO4 catalyst. Among these ternary photocatalysts, S35A65(300) exhibited the most excellent photocatalytic performance under visible light irradiation, which could be mainly attributed to synergy effect of the notably improved separate efficiency of photogenerated electron-hole pairs and the suitable stop-bands of 3DOM-SrTiO3(300) material. Although the gradually reduced activity in cycling tests was obtained over S35A65(300) under visible light irradiation, an excellent durability could be achieved for S35A65(300) under UV–vis light irradiation. No obvious loss in photocatalytic efficiency was observed after six cycles for RhB degradation. The notably improved enhanced durability of 3DOM-SrTiO3/Ag/Ag3PO4 ternary composites under UV–vis light irradiation could be mainly attributed to the Z-scheme mechanism of this ternary composite photocatalyst.
Keywords: 3DOM-SrTiO3/Ag/Ag3PO4 ternary composites; Inverse opal; Z-scheme photocatalyst; Slow photon effect; Photodegradation;
Photodegradation of sulfonamides by g-C3N4 under visible light irradiation: Effectiveness, mechanism and pathways by Yali Song; Jiayu Tian; Shanshan Gao; Penghui Shao; Jingyao Qi; Fuyi Cui (88-96).
Display OmittedFor the first time, the photocatalytic degradation of sulfamethoxazole (SMX), sulfisoxazole (SSX), sulfadiazine (SDZ), sulfamerazine (SMZ) by g-C3N4 under visible light irradiation was investigated. Results revealed that compared to photolysis, the photocatalytic degradation efficiencies of the four sulfonamides were significantly enhanced with the addition of g-C3N4, and more than 90% of photodegradation removal was obtained. The effects of typical water quality parameters, including solution pH, bicarbonate ion and humic acid, on the photodegradation process were discussed. It was found that although the photodegradation of the four sulfonamides exhibited different trends under the variation of the water quality parameters, an excellent photocatalytic removal could always be achieved, illustrating the robustness and effectiveness of the g-C3N4 photodegradation process. The ESR measurements showed that both OH• and •O2 − were produced in the photocatalytic process of g-C3N4 under visible light irradiation. And trapping experiments confirmed that •O2 − and holes played a significant role in the photodegradation of SMX, SDZ and SMZ; but holes and OH• were the main oxidative species for SSX degradation. Finally, according to the oxidation products detected by ultra-high performance liquid chromatography-tandem mass spectrometric (UPLC/MS/MS), the degradation pathways of the four sulfonamides were proposed and compared. It was found that there were some common pathways shared by the different sulfonamides, such as cleavage of S-N bond and hydroxylation of the benzene ring (the main degradation pathways for SSX). More importantly, some specific photodegradation pathways were also identified: (1) the nitration of amino group on the benzene ring occurred for SMX, SDZ and SMZ (the main degradation pathway for SMX, SDZ and SMZ), but not for SSX; (2) the bond cleavage between benzene ring and S occurred only in degradation of SSX; and (3) the carboxylation of the methyl group occurred only in degradation of SMZ.
Keywords: Visible light; Photocatalytic degradation; g-C3N4; Sulfonamides;
A simple combustion method for the synthesis of multi-functional ZrO2/CuO nanocomposites: Excellent performance as Sunlight photocatalysts and enhanced latent fingerprint detection by L. Renuka; K.S. Anantharaju; Y.S. Vidya; H.P. Nagaswarupa; S.C. Prashantha; S.C. Sharma; H. Nagabhushana; G.P. Darshan (97-115).
Display OmittedA facile solution combustion synthesis has been adopted to synthesize ZrO2/CuO nanocomposite oxides (NCO’s) by utilizing Oxalyl dihydrazide (ODH) as fuel. The X-ray diffraction patterns and TEM analysis reveals the presence of cubic ZrO2 and CuO in ZrO2/CuO NCO’s. The NCO’s synthesized by simple, fast, highly sensitive and low-cost method is found to be an alternate to traditional luminescent powders for the detection and enhancement of finger marks in a broad range of surfaces. The photoluminescence analysis indicates that the present NCO is an effective blue component in display applications. The synthesized ZrO2/CuO (2:1) composite exhibited excellent photocatalytic activity towards the degradation of various dyes under Sunlight. In particular, Indigo carmine dye was chosen to explore the photocatalytic performance of prepared NCO’s under Sunlight illumination. It was found that ZrO2:CuO (2:1) NCO showed enhanced photocatalytic activity of 97% which was found to be 3.3 times 2.4 times and 1.5 times higher than that of pure ZrO2, CuO and commercial P25. This can be mainly attributed to the balance between the parameters, band gap, nature of morphology, crystallite size, defects and surface area which causes a slow electron-hole pair recombination rate with fast electron transfer ability. It opens new window to use this simple method to synthesize multifunctional character ZrO2-based composite materials in the area of photocatalysis particularly waste water treatment, display applications as well as a labeling agent to enhance latent fingerprints.
Keywords: ZrO2/CuO nanocomposite oxides; Photocatalysis; Photoluminescence; Fingerprint detection;
Deactivation mechanism and regeneration of carbon nanocomposite catalyst for acetylene hydrochlorination by Xingyun Li; Pan Li; Xiulian Pan; Hao Ma; Xinhe Bao (116-120).
Display OmittedAcetylene hydrochlorination is an important coal-based technology for production of vinyl chloride, the monomer of one of the world mostly used plastics. Despite of the great potentials demonstrated for carbon-based catalysts to replace the toxic mercury chloride, the stability and the deactivation mechanism are rarely discussed, which is essential for real applications. Herein, we present a detailed study on the deactivation mechanism of nitrogen doped carbon based catalyst in acetylene hydrochlorination. The results show that the deactivation was likely caused by the carbon-like deposition over the catalyst, which can be regenerated with high temperature NH3 treatment.
Keywords: Acetylene hydrochlorination; Metal free; Carbon catalysis; Carbon deposit; Catalyst regeneration;
Carbon nanotube supported PdAg nanoparticles for electrocatalytic oxidation of glycerol in anion exchange membrane fuel cells by Neeva Benipal; Ji Qi; Qi Liu; Wenzhen Li (121-130).
Display OmittedElectro-oxidation of alcohol is the key reaction occurring at the anode of a direct alcohol fuel cell (DAFC), in which both reaction kinetics (rate) and selectivity (to deep oxidation products) need improvement to obtain higher power density and fuel utilization for a more efficient DAFC. We recently found that a PdAg bimetallic nanoparticle catalyst is more efficient than Pd for alcohol oxidation: Pd can facilitate deprotonation of alcohol in a base electrolyte, while Ag can promote intermediate aldehyde oxidation and cleavage of C―C bond of C3 species to C2 species. Therefore, a combination of the two active sites (Pd and Ag) with two different functions, can simultaneously improve the reaction rates and deeper oxidation products of alcohols (Applied Catalysis B, 2016, 199, 494). In this continuing work, Pd, Ag mono, and bimetallic nanoparticles supported on carbon nanotubes (Ag/CNT, Pd/CNT, Pd1Ag1/CNT, and Pd1Ag3/CNT) were prepared using an aqueous-phase reduction method; they served as working catalysts for studying electrocatalytic oxidation of glycerol in an anion-exchange membrane-based direct glycerol fuel cell. Combined XRD, TEM, and HAADF-STEM analyses performed to fully characterize as-prepared catalysts suggested that they have small particle sizes: 2.0 nm for Pd/CNT, 2.3 nm for PdAg/CNT, 2.4 nm for PdAg3/CNT, and 13.9 nm for Ag/CNT. XPS further shows that alloying with Ag results in more metal state Pd presented on the surface, and this may be related to their higher direct glycerol fuel cell (DGFC) performances. Single DGFC performance and product analysis results show that PdAg bimetallic nanoparticles can not only improve the glycerol reaction rate so that higher power output can be achieved, but also facilitate deep oxidation of glycerol so that a higher faradaic efficiency and fuel utilization can be achieved along with optimal reaction conditions (increased base-to-fuel ratio). Half-cell electrocatalytic activity measurement and single fuel cell product analysis of different glycerol oxidation intermediates, including C3: glycerate, tartronate, mesoxalate, and lactate; C2: glycolate and oxalate, over PdAg/CNT catalyst was further conducted and produced deeper insight into the synergistic effects and reaction pathways of bimetallic PdAg catalysts in glycerol electrocatalytic oxidation.
Keywords: Biomass renewables; Glycerol oxidation; Anion-exchange membrane fuel cell; PdAg nanoparticles; Electrocatalysis;
CO2 capture and photocatalytic reduction using bifunctional TiO2/MOF nanocomposites under UV–vis irradiation by Angus Crake; Konstantinos C. Christoforidis; Andreas Kafizas; Spyridon Zafeiratos; Camille Petit (131-140).
Display OmittedTiO2 nanosheets and metal-organic framework (NH2-UiO-66) were effectively coupled via an in‐situ growth strategy to form bifunctional materials for the combined capture and photocatalytic reduction of CO2 under UV–vis light irradiation. This was done to take advantage of the high CO2 adsorption capacity of the MOF and the photocatalytic properties of pre-formed TiO2 nanosheets in a single material. The prepared materials were thoroughly characterized using a variety of techniques. They were subsequently tested for CO2 adsorption and CO2 photocatalytic reduction using a heterogeneous gas/solid set-up to imitate both CO2 capture and fixation in a single process. The adopted synthesis process allowed the development of a tight interaction between TiO2 and NH2-UiO-66 forming a heterojunction, while maintaining both the high CO2 uptake and porosity of NH2-UiO-66. The nanocomposites were proven durable and significantly more efficient in reducing CO2 to CO than their single components. Photocatalytic activity was greatly affected by the nanocomposites composition with the optimum TiO2 content doubling the CO evolution rate compared with the pure TiO2. The improved photoactivity was assigned to the enhanced abundance of long lived charge carriers, as revealed by transient absorption spectroscopy (TAS). This most likely occurred due to the effective charge transfer via interface. A possible mechanism is discussed on the basis of the combined catalytic, spectroscopic and CO2 adsorption results.
Keywords: Metal-organic frameworks; Titanium dioxide; Photocatalysis; Carbon dioxide; Reduction;
CeO2-x platelet from monometallic cerium layered double hydroxides and its photocatalytic reduction of CO2 by Ting Ye; Weimin Huang; Liming Zeng; Mengli Li; Jianlin Shi (141-148).
Display OmittedMonometallic cerium layered double hydroxides (MCe-LDHs) were successfully synthesized for the first time through a simple approach. XRD, TEM, SEM, XPS, FT-IR, TG-DSC techniques and UV–vis diffuse reflectance spectroscopy were used to characterize the samples. The obtained MCe-LDHs showed typical layered structure composing of quasi-hexagonal platelets with side length of about 2 μm and thickness about tens of nanometers, and preserved its platelet morphology after heat treatment at up to 800 °C. Our study also revealed that the heat-treatments at different temperatures could be employed to tune the concentration ratio of Ce3+/Ce4+ and the surface area of those cerium oxide platelets, both of which play a key role in the photocatalytic activity towards photoreduction of CO2.
Keywords: Monometallic cerium layered double hydroxides; Cerium oxide platelets; CO2 photoreduction;
Efficient photocatalytic hydrogen production over La/Rh co-doped Ruddlesden-Popper compound Sr2TiO4 by Xiaoqin Sun; Xiaoxiang Xu (149-159).
Display OmittedLa/Rh can be successfully co-doped into Sr2TiO4 at a synthesis temperature as low as 900 °C. The presence of Rh inside Sr2TiO4 greatly improves its visible light absorbance and photocatalytic activity while co-doping La helps to build a charge compensated system. The origin of visible light absorption and photocatalytic activity stems from a newly formed valence band with mainly Rh 4d character inside the band gap of Sr2TiO4.Layered semiconductor compounds often exhibit intriguing properties for photocatalytic water splitting, probably correlated with their peculiar crystal structures that facilitate charge separations. In this work, we perform an investigation on the layered Ruddlesden-Popper compound Sr2TiO4 and its La/Rh co-doped counterparts for photocatalytic hydrogen production from water. Their crystal structures, optical absorption and other physicochemical properties have been systematically explored. Our results suggest that La/Rh can be successfully incorporated into Sr2TiO4 with layered crystal structure maintained. The use of polymerized-complex method for sample synthesis significantly reduces the calcination temperature as low as 900 °C. La/Rh serves as efficient dopants for extending the light absorbance of Sr2TiO4 as far as 550 nm. Photocatalytic hydrogen productions are also considerably improved after La/Rh co-doping under both full range (λ ≥ 250 nm) and visible light irradiation (λ ≥ 420 nm). An optimal doping level is reached at 3% (Sr1.97La0.03Ti0.97Rh0.03O4) which gives the highest average hydrogen production rate ∼100 μmol/h and ∼40 μmol/h under full range (λ ≥ 250 nm) and visible light irradiation (λ ≥ 420 nm), corresponding to apparent quantum efficiency ∼1.27% and ∼1.18%, respectively. Photoelectrochemical analysis reveals that charge separation and electron lifetime strongly depends on the level of La/Rh co-doping. Mott-Schottky analysis and theoretical calculations indicate that the improved light absorption of La/Rh co-doped Sr2TiO4 stems from the formation of new valence band with Rh 4d character which uplifts the valence band edge of Sr2TiO4.
Keywords: Photocatalyst; Hydrogen production; Ruddlesden-Popper compound; Rh doping; DFT calculation;
MoS2 quantum dots-interspersed Bi2WO6 heterostructures for visible light-induced detoxification and disinfection by Xiangchao Meng; Zizhen Li; Haoming Zeng; Jie Chen; Zisheng Zhang (160-172).
Display OmittedMoS2 Quantum dots-interspersed Bi2WO6 heterostructure is fabricated for photocatalytic applications for the first time. It exhibits enhanced visible light-driven photocatalytic detoxification and disinfection in wastewater compared to bare Bi2WO6 and MoS2. MoS2 quantum dots as a co-catalyst applied in photocatalysis oxidation possesses multiple merits: (1) noble-metal-free; (2) high mobility of photogenerated charge carriers; (3) high adsorption capacity and (4) improved capture capacity of visible light photons. Electron-hole separation rate which is critical for an efficient photocatalysis is greatly improved via the built-in electric field of p-n heterostructure and the quantum dots interspersed on the surface. This work shed a light on loading MoS2 quantum dots as a co-catalyst on a support aiming to significantly improve its photocatalytic performance in organic pollutants degradation and bacteria inactivation.
Keywords: Photocatalysis; Bi2WO6; MoS2; Quantum dot;
Fish-scale structured g-C3N4 nanosheet with unusual spatial electron transfer property for high-efficiency photocatalytic hydrogen evolution by Bo Lin; Hua An; Xiaoqing Yan; Tianxi Zhang; Jinjia Wei; Guidong Yang (173-183).
Display OmittedGrafing the structures in nature onto g-C3N4 is an interesting and fascinating protocol to highly optimize its performances. Herein, a novel opened-up fish-scale structured g-C3N4 nanosheet has been synthesized via a simple one-step solvothermal method for photocatalytic hydrogen evolution. The unique fish-scale structure endows g-C3N4 with unusual spatial electron transfer property, which means that the photogenerated electrons selectively migrate along the flat direction to the edges of fish-scale flakes. This property well reveals the transfer path of photogenerated charges and the origin of high charge separation efficiency in photocatalytic reaction, thus yielding a remarkable catalytic activity (a hydrogen-evolution rate of 1316.35 μ mol h−1 g−1), nearly 20 and 2.93 times higher than that of bulk g-C3N4 and exfoliated g-C3N4 nanosheet. Besides, the fish-scale structured g-C3N4 also owns a superior durability and stability, indicating an outstanding potential application in solar fuel production. The research results would provide a platform for the design and construction of high-performance photocatalysts with highly-efficient charge separation.
Keywords: Fish-scale; g-C3N4; Nanosheet; Unusual spatial electron transfer; Photocatalytic hydrogen evolution;
Fabrication of TiO2 hollow microspheres assembly from nanosheets (TiO2-HMSs-NSs) with enhanced photoelectric conversion efficiency in DSSCs and photocatalytic activity by Ruiwen Yang; Jinghua Cai; Kangle Lv; Xiaofeng Wu; Wenguang Wang; Zhihua Xu; Mei Li; Qin Li; Weiqing Xu (184-193).
Display OmittedFabrication of TiO2 hollow microspheres (TiO2-HMSs) with complex structure is of great importance but remains a great challenge. In this paper, hierarchical TiO2 hollow microspheres assembly from nanosheets (TiO2-HMSs-NSs) were prepared by hydrothermal treatment of TiO2-HMSs precursor in NaOH solution and followed by acid wash and calcination. The effect of hydrothermal reaction time on the structure and photoelectric conversion performances of TiO2-HMSs-NSs film solar cells was systematically studied. It was found that both the BET surface area and photocatalytic activity of TiO2-HMSs-NSs, in photocatalytic degradation of Brilliant Red X-3B dye, are positively related to the hydrothermal reaction time (from 0 to 3 h). The BET specific area of TiO2-HMSs-NSs steady increase from 21 m2 g−1 of TiO2-HMSs precursor (H0) to 184 m2 g−1 (H3), improved by a factor of 8.76, while the photocatalytic activity of H3 increased 7.50 times when compared with that of H0 sample. The highest photoelectric conversion efficiency (5.97%) of TiO2-HMSs-NSs film solar cell was obtained for H2 sample, exceeding that of TiO2-HMSs precursor (H0) based film solar cell (3.75%) with the same film thickness by a factor of 1.6. The improved photoelectric conversion efficiency of TiO2-HMSs-NSs based solar cell was attributed to the unique hierarchical hollow structure, which results in a good contact between TiO2 and FTO glass, enlarged pore volume, enhanced adsorption to sensitizer and improved light scattering ability.
Keywords: TiO2; Hollow microspheres; Dye-sensitized solar cells (DSSCs); Photocatalysis;
Carbon nitride coupled with CdS-TiO2 nanodots as 2D/0D ternary composite with enhanced photocatalytic H2 evolution: A novel efficient three-level electron transfer process by Zhifeng Jiang; Kun Qian; Chengzhang Zhu; Hongli Sun; Weiming Wan; Jimin Xie; Huaming Li; Po Keung Wong; Shouqi Yuan (194-204).
Carbon nitride coupled with CdS-TiO2 nanodots as 2D/0D ternary composite with enhanced photocatalytic H2 evolution: A novel efficient three-level electron transfer process.Display OmittedPhotocatalytic H2 evolution from water splitting requires an efficient photocatalyst with excellent charge separation ability and broad visible-light adsorption region. 0D CdS-TiO2 nanodots (NDs) were successfully decorated on the 2D g-C3N4 sheets via an epitaxial growth process. The as-synthesized ternary composite of CdS-TiO2@g-C3N4 exhibits enhanced visible-light-driven photocatalytic H2 evolution activity, as compared to the binary composites and their single components, which is about 6.7 and 11.2 times higher than those of single CdS and g-C3N4, respectively. Moreover, the as-obtained ternary composite has an external quantum efficiency (EQE) of 11.9% at 420 nm, implying the high utilization efficiency of photo-induced charges. In addition, the superior photostability can be achieved by this coupling method. The enhanced photocatalytic activity was attributed to the efficient charge separation originated from the three-level electron transfer system, the matched energy level positions, the abundant adsorption sites and active sites (0D/2D structure) and the synergistic effect among CdS, TiO2 and g-C3N4. The work present here demonstrated that the construction of this three-level electron transfer system is an effective strategy to design more efficient ternary materials toward solar energy conversion (like H2 production and CO2 reduction).
Keywords: TiO2-CdS nanodots; Carbon nitride; Photocatalysis; H2-generation;
Ni3(C3N3S3)2 coordination polymer as a novel broad spectrum-driven photocatalyst for water splitting into hydrogen by Feng Guo; Weilong Shi; Sijie Guo; Weisheng Guan; Yanhong Liu; Hui Huang; Yang Liu; Zhenhui Kang (205-211).
Display OmittedWe have successfully synthesized a novel Ni3(C3N3S3)2 coordination polymer by a facile wet-chemical rout for the first time. Specifically, the as-prepared Ni3(C3N3S3)2 possessed UV–vis-NIR broad spectrum absorption and can be acted as a board spectrum-driven photocatalyst for water splitting into hydrogen. As expected, the H2 production performance from pure water over Ni3(C3N3S3)2 was realized through from UV (λ < 400 nm) to Vis (400 ≤ λ ≤ 760 nm) and NIR (λ > 760 nm) without any sacrificial agents or cocatalysts, and the amounts of H2 production are 65.3, 53.9 and 16.3 μmol corresponding to UV, Vis and NIR irradiation after 24 h, respectively. Significantly, the efficiency of H2 production and the stability over the Ni3(C3N3S3)2 could be improved with the assistance of triethanolamine. And the average H2 evolution efficiencies on Ni3(C3N3S3)2 were efficaciously increased by around 2-fold with the H2 production value of 112.6, 93.3 and 30.1 μmol for 24 h under the UV, Vis and NIR light exposure, respectively.Sparked by the increasing energy crisis, much research has been focused on seeking board spectrum-driven photocatalysts for water splitting. Herein, the Ni3(C3N3S3)2 coordination polymer was firstly synthesized by a simple wet-chemical method, as a novel board spectrum-driven photocatalyst for water splitting. The as-prepared Ni3(C3N3S3)2 exhibited excellent photocatcalytic H2-producing activity from the half-reaction of water splitting without the help of any sacrificial agents or cocatalysts, and the amounts of H2 production are 65.3, 53.9 and 16.3 μmol corresponding to UV (λ < 400 nm), visible (400 ≤ λ ≤ 760 nm) and near-infrared (λ > 760 nm) irradiation after 24 h, respectively. Another valuable finding is that after adding triethanolamine as a sacrificial donor, the average H2 evolution efficiencies on Ni3(C3N3S3)2 were efficaciously increased by around 2-fold with the H2 production value of 112.6, 93.3 and 30.1 μmol for 24 h under the UV light, visible light and near-infrared light exposure, respectively. More importantly, the stability of Ni3(C3N3S3)2 was effectively improved by means of triethanolamine. The results facilitate the increasing attention of narrow band gap non-noble metal coordination polymers treated as board spectrum-driven photocatalysts for expanding the utilization of solar light.
Keywords: Coordination polymer; Photocatalyst; Ni3(C3N3S3)2; Water splitting; Board spectrum-driven;
Hydrogen production from formic acid dehydrogenation over Pd/C catalysts: Effect of metal and support properties on the catalytic performance by Hyo-jin Jeon; Young-Min Chung (212-222).
Display OmittedWhile formic acid dehydrogenation has become one of the most promising strategies for hydrogen storage, the crucial factors for realizing an efficient catalyst remain controversial. In this study, a range of Pd/C catalysts were systematically prepared by adopting either diverse metal deposition methods or different acid treatments, and the resulting catalysts were used for formic acid dehydrogenation under ambient conditions without additives. The volcano-type dependence of the activity on the Pd particle size, rate enhancement over Pd with smaller / ratios, and superior activity of Pd0 or Pd0/Pd(OH)2 mixture to Pd2+ clearly indicate that not only the particle size but also the surface structure or electronic states of active metal would be of prime importance to promote the reaction. Moreover, another volcano relation between the activity and the pH of a reaction solution determined by the functional groups of an acid-treated support obviously suggests that the catalytic activity is very sensitive to pH, and that a neutral reaction solution is preferred to maximize the catalytic performance. The unprecedented critical effect of a support on the catalytic performance may be rationalized in terms of two factors: (i) recombination of the formate ion with a proton and/or delay of formic acid deprotonation by excess protons in an acidic solution; (ii) competitive adsorption between the formate and hydroxyl ions in a basic solution. Therefore, tuning the nature of a support to achieve a balance between the two competitive factors is important to enhance the catalytic performance.
Keywords: Pd/C; Formic acid; Dehydrogenation; Hydrogen; Hydrogen storage;
Synergistic effect between copper and cerium on the performance of Cu x -Ce0.5-x -Zr0.5 (x = 0.1–0.5) oxides catalysts for selective catalytic reduction of NO with ammonia by Sher Ali; Liqiang Chen; Fulong Yuan; Rui Li; Tianrui Zhang; Syed ul Hasnain Bakhtiar; Xuesong Leng; Xiaoyu Niu; Yujun Zhu (223-234).
Cu0.2-Ce0.3-Zr0.5 exhibits high NH3-SCR activity of NO in the range of 150–270 °C even at high GHSV due to the strong interaction between Cu and Ce leading to the improvement of the acidity and redox property.Display OmittedA series of Cu x -Ce0.5-x -Zr0.5 oxides catalysts with different Cu/Ce ratio were synthesized by citric acid method. The catalysts were characterized by XRD, BET surface area, H2-TPR, NH3-TPD, NO-TPD, XPS and in-situ DRIFTS. The synergistic effect between copper and cerium on the catalytic performance of Cu x -Ce0.5-x -Zr0.5 for selective catalytic reduction of NO with ammonia was investigated. It was found that the Cu0.2-Ce0.3-Zr0.5 catalyst show the excellent SCR activity, N2 selectivity and H2O/SO2 durability in a low temperature range of 150–270 °C even at high gas hourly space velocity of 84,000 h−1. The strong interaction leads to the improvement of the acidity and the increase in the amount of active oxygen species (oxygen vacancy), which are responsible for the higher activity at low temperatures. The SCR reaction process over Cu0.2-Ce0.3-Zr0.5 was also examined using in-situ DRIFTS. The DRIFTS results indicate that abundant ionic NH4 + (Brønsted acid sites), coordinated NH3 on the Lewis acid sites, as well as highly active monodentate nitrate and bridging nitrate species were the key intermediates in the SCR reaction.
Keywords: Synergistic effect; Selective catalytic reduction; NO; Cu x -Ce0.5-x -Zr0.5 Oxides;
Review of recent trends in photoelectrocatalytic conversion of solar energy to electricity and hydrogen by Panagiotis Lianos (235-254).
“Review of recent trends in photoelectrocatalytic conversion of solar energy to electricity and hydrogen” by P. Lianos.Display OmittedThis work is a review of the recent trends in the photoelectrocatalytic conversion of solar energy into electricity or hydrogen. It focuses on photocatalytic fuel cells and photoelectrocatalytic water splitting systems and presents both the basic principles and the design of devices. It includes a broad review of materials employed for the construction of photoanodes, photocathodes and tandem cells and highlights the related research fields which are expected to be of interest in the near future. The review is intended to become a basic manual for new adepts to the field and at the same time a handy reference to experienced researchers.
Keywords: Photoelectrocatalytic; Photoelectrochemical; Hydrogen; Water splitting; Photocatalytic fuel cells;
Halo-organic pollutants: The effect of an electrical bias on their decomposition mechanism on porous iron electrodes by Eitan J.C. Borojovich; Ronen Bar-Ziv; Olga Oster-Golberg; Hen Sebbag; Michael Zinigrad; Dan Meyerstein; Tomer Zidki (255-262).
Display OmittedThe de-halogenation processes of CH2BrCHBrCOO− and of CH2ClCH(OH)COO− on Zero Valent Iron (ZVI) powders and porous iron electrodes were studied. The results suggest that by applying a negative voltage bias on the electrode, the composition of the products obtained is dramatically changed. Furthermore, the applied potential inhibits the passivation of the ZVI. Thus, it is recommended that the application of a negative potential to porous ZVI is desirable in batch treatment of halo-organic pollutants.
Keywords: ZVI; Porous electrode; De-halogenation; Electrical bias;
Photo enhanced methanol electrooxidation: Further insights into Pt and TiO2 nanoparticle contributions by Christopher Odetola; Liliana N. Trevani; E. Bradley Easton (263-275).
Display OmittedPt nanoparticles (PtNPs) were deposited on two different supports: Vulcan® XC-72R carbon (PV) and TiO2/G-PV, a TiO2/carbon composite support prepared using glucose-doped Vulcan® XC-72R carbon (G-PV). The presence of TiO2 has been shown to maximize the PtNPs specific surface area and improves the catalytic performance through Pt-metal oxide interaction. The catalytic activity of Pt/TiO2/G-PV and Pt/PV toward the methanol oxidation reaction (MOR) was investigated with and without ultraviolet-visible (UV–vis) light irradiation using different electrochemical techniques. The results show the enhancement in catalytic activity in Pt/PV under illumination (Ipeak illumination-Ipeak dark)*100/Ipeak dark ∼ 100%) can be attributed to a significant reduction in the charge transfer resistance (Rct) when the electrode is illuminated (635 Ω (dark) vs 84 Ω (illumination)) as determined by electrochemical impedance spectroscopy (EIS). The observed photo enhancement is relatively modest when compared to the Pt/TiO2/G-PV catalyst (Ipeak illumination-Ipeak dark)*100/Ipeak dark ∼ 171%), even though the change in the Rct (185 Ω vs. 99 Ω) is not as pronounced as in the Pt/PV samples. The carbon monoxide (CO) stripping results indicate that illumination aids the removal of adsorbed CO from the PtNPs surface. The remarkable enhancement on the oxidation of methanol under UV–vis illumination in the case of the Pt/TiO2/G-PV catalyst materials show the potential of these materials for applications such as disposable and portable electrochemical sensors for water analysis, mainly the determination of organic contaminants in water. Moreover, it can be a breakthrough in the development of novel photoelectrochemical ethanol sensors and a new generation of energy conversion devices.
Keywords: Glucose; Titanium oxide; Methanol oxidation; Photo radiation; Charge transfer resistance; Electrochemical impedance spectroscopy;
A catalytic approach to synthesis of PLP analogs and other environmental protocols in a single handed CaO/TiO2 green nanoparticle by Sk Jahir Abbas; P.V.R.K. Ramacharyulu; Hsin-Hsi Lo; Sk Imran Ali; Shyue-Chu Ke (276-289).
Display OmittedAs our precursory stage we have focus straight forward on clean catalytic approach for the production of C3 substituted pyridoxal-5′-phosphate analogues of vitamin B6, and other environmental protocols like photocatalytic activity, green fossil fuels and c–c coupling using efficient biocompatible eggshell related unrivalled materials which show versatility of the catalytic effect on different inorganic support. The eggshell immobilized nanoparticles have encouraging relevance in creation of new molecules and can advantageously be studied by various spectroscopic, thermal and elemental analyses like powder X-ray diffraction (XRD), Raman spectroscopy, UV–vis, Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area analysis. The elucidate nature of nanoparticles offer: more active site acts as lewis acid, vacancies on the catalyst surface and good to better yield of C3 substituted deoxy and 2-nor deoxy coenzyme pyridoxine (PN), coupling products propargylamines (PA), photo degrading enhancement of MB and nucleophilic substituted fatty acid (BD). This enzyme cofactor explore molecular synthons to synthetic equivalent: 3-deoxy and 2-nor-3-deoxy pyridoxal (PL), pyridoxal oxime (PO), pyridoxamine (PM) and mono phosphate derivative of 3-deoxyPM, 3-deoxyPL respectively and chemistry of selective oxidation and schiff base mechanism was studied and complemented through combined experimental and theoretical molecular orbital calculation consequently. The heterogeneous catalyst has strong selective ability towards selective reducing pyridine diester, bioactive intermediates substances and holds vast potential towards separation for the photogenerated electron-hole pairs and renewable, nontoxic, biodegradable green fossil fuels. The catalyst including environmental concern is reapplicable and strong impressive that can unfold the space of worthy metal component widely and facilitate the scope to take a vital role in different fileds like catalysis, biochemistry, nanoscience, energy and materials science.
Keywords: Green catalysis; Pyridoxal-5′-phosphate; Reduction and selective schiff base mechanism; A3 coupling; Photocatalytic activity; Fatty acid esters;
One-step synthesis of CdS nanoparticles/MoS2 nanosheets heterostructure on porous molybdenum sheet for enhanced photocatalytic H2 evolution by Lili Zhao; Jin Jia; Zhiyuan Yang; Jiayuan Yu; Aili Wang; Yuanhua Sang; Weijia Zhou; Hong Liu (290-296).
Display OmittedCo-catalysts for H2 production are often made from expensive noble metals, such as the most efficient Pt. The alternative non-noble metal co-catalysts with low cost and high efficiency are therefore highly desirable for economically viable H2 production. Herein, we demonstrated that a CdS/MoS2/Mo sheets system simultaneously containing photocatalysts, co-catalysts, and conductive supports, was prepared via the one-step hydrothermal process by Mo sheets as template and Mo sources. The obtained CdS/MoS2/Mo sheets possess the superior photocatalytic H2 production via water splitting under visible light irradiation, which achieved an extraordinary H2 production of 4540 μmol h−1 g−1, up to 28.6 and 3.6 times greater than that of CdS alone and Pt/CdS. The synergetic effect of MoS2 as co-catalysts and Mo sheets as conductive supports contribute to the dramatically improved photocatalytic H2 evolution activity of CdS photocatalysts, by means of facilitating charge carriers separation and providing active sites for proton reduction. These findings provide a straightforward and practical route to produce cheap and efficient co-catalysts for large-scale water splitting.
Keywords: Co-catalysts; Non-noble metal; Conductive supports; Photocatalytic H2 evolution; Porous;
Plasmon enhancement on photocatalytic hydrogen production over the Z-scheme photosynthetic heterojunction system by Hongqing Gao; Peng Zhang; Jiangtao Zhao; Yongshang Zhang; Junhua Hu; Guosheng Shao (297-305).
We reported direct evidence of plasmon enhancement on photocatalytic hydrogen production over the Z-scheme photosynthetic heterojunction system.Display OmittedDirect evidence of plasmon for enhanced H2 production is observed in photocatalytic water reduction by using TiO2/WO3 electrospun nanofibers decorated with Au nanoparticles. The H2 production rate of the as-prepared composite nanofibers was greatly enhanced compared with pure TiO2 nanofibers (S0) and TiO2/WO3 nanofibers (S1). The enhanced activities were mainly attributed to the Schottky effect and Z-scheme photosynthetic heterojunction system, in this system, WO3 as a hole collector and Au as an electron collector, promoting effective charge separation. More importantly, Surface Plasmon Resonance (SPR) effect of Au further promoted charge separation and absorption of visible light. On the basis of the Z-scheme photosynthetic heterojunction system, the synergistic effect of Schottky and SPR effect further improve the performance of photocatalytic H2 production, which were directly evidenced by photocurrent, electrochemical impedance spectroscopy (EIS) and ultraviolet Photoelectron Spectrometer (UPS) analysis. Besides, the synthesis route delivered three-dimensional sheets on the basis of interwoven nanofibrous networks, which can be readily recycled for the circular application of a potent photocatalyst system.
Keywords: Electrospinning; Z-scheme; Photocatalysis; Hydrogen production; Synergistic effect;
The effect of the surface disordered layer on the photoreactivity of titania nanoparticles by J. Soria; J. Sanz; M.J. Torralvo; I. Sobrados; C. Garlisi; G. Palmisano; S. Çetinkaya; S. Yurdakal; V. Augugliaro (306-319).
Display OmittedIt is well known that the surface of metal oxide catalysts presents, usually, non-crystalline species containing impurities and low coordinated cations, which are observed in HRTEM images as a disordered layer of amorphous phase. Despite of being these species more accessible and less stable than the crystalline catalysts components, they have been rarely considered when analysing the catalyst activity. In this work, we have studied the effect of a treatment with HCl solution at pH = 0 on the characteristics of the disordered layer in two commercial anatase TiO2 samples, using techniques such as TGA, 1H MAS-NMR and HRTEM, and by determining these sample photocatalytic activity for the 4-nitrophenol degradation in aqueous suspension. The results indicate that associations of chlorine ions in amorphous titania chains and hydrated excess protons structures interact with anatase bridging hydroxyls. This interaction, that breaks Ti―O―Ti bonds between the anatase particles and the disordered layer species, enhances the anatase hydroxyls acidity, favouring the formation of O− radicals and eventually increasing the photocatalytic activity for 4-nitrophenol degradation under UV irradiation.
Keywords: TiO2 acid treatment; Titania modifications; Disordered titania layer; Photocatalytic activity enhancement; 4-Nitrophenol degradation;
Photocatalytic H2 evolution with a Cu2WS4 catalyst on a metal free D-π-A organic dye-sensitized TiO2 by Emre Aslan; Mehmet Kerem Gonce; Mesude Zeliha Yigit; Adem Sarilmaz; Elias Stathatos; Faruk Ozel; Mustafa Can; Imren Hatay Patir (320-327).
Display OmittedA noble metal free Cu2WS4 catalyst and two donor-π-bridge-acceptor metal-free dyes are investigated for photocatalytic hydrogen evolution.A system comprising of a noble metal free Cu2WS4 catalyst and donor-π-bridge-acceptor metal-free organic dyes (MZ-341 and MZ-235) sensitized TiO2 has been reported for the photocatalytic hydrogen production using triethanolamine (TEOA) as the sacrificial reagent under visible light irradiation. Cu2WS4 nanocubes were synthesized according to hot-injection reaction technique. The structural properties of the Cu2WS4 nanocubes were examined by microscopy (HR-TEM) and XRD techniques where the formation of nanocubes (rectangular and square cubes) with average edge length to be ranged from 100 to 500 nm and tetragonal phase (I-42m) was proved respectively. It was found that MZ-341 and MZ-235 dyes sensitized TiO2 have been produced 661 μmol g−1 h−1 and 531 μmol g−1 h−1 hydrogen, respectively in TEOA solution at pH 9. When Cu2WS4, was used as a co-catalyst, hydrogen evolution by MZ-341 and MZ-235 sensitized TiO2 have been slightly increased to 1406 μmol g−1 h−1 and 943 μmol g−1 h−1, respectively.
Keywords: Hydrogen evolution; Hot-injection; Cu2WS4 catalyst; Dye sensitization;
Structure-activity relationships of Ni-Cu/Al2O3 catalysts for γ-valerolactone conversion to 2-methyltetrahydrofuran by Iker Obregón; Inaki Gandarias; Ainhoa Ocio; Iker García-García; Nerea Alvarez de Eulate; Pedro L. Arias (328-341).
Display OmittedThe activity of a series of impregnated Ni-Cu/Al2O3 catalysts was evaluated for the production of 2-methyltetrahydrofuran (MTHF) from γ-valerolactone using 2-butanol as solvent. These catalysts evidenced that their activities depend more on the metal phase nature then on the metal sites dispersion, achieving three times higher Normalized MTHF Productivity (NMP) the samples with the highest amounts of the Ni-Cu alloy. In addition, the activity of those high Ni-Cu alloy containing samples showed to be limited by their low surface acidity. The promotion of the alloy formation, acidity and metal-acid sites proximity was achieved by a co-precipitation method. This new catalyst, calcined and reduced at 450 °C, allows a MTHF yield of 64% after 5 h. The tested catalysts showed deactivation by carbon deposition which could be overcome by intermediate regeneration between runs. The best catalyst showed stable > 54% MTHF yield for three consecutive runs.
Keywords: 2-Methyltetrahydrofuran; γ-valerolactone; Biofuel; Hydrogenolysis;
The role of cobalt hydroxide in deactivation of thin film Co-based catalysts for sodium borohydride hydrolysis by M. Paladini; G.M. Arzac; V. Godinho; D. Hufschmidt; M.C. Jiménez de Haro; A.M. Beltrán; A. Fernández (342-351).
Display OmittedDeactivation of a Co catalyst prepared as thin film by magnetron sputtering was studied for the sodium borohydride (SB) hydrolysis reaction under different conditions. Under high SB concentration in single run experiments, the formation of a B-O passivating layer was observed after 1.5 and 24 h use. This layer was not responsible for the catalyst deactivation. Instead, a peeling-off mechanism produced the loss of cobalt. This peeling-off mechanism was further studied in cycling experiments (14 cycles) under low SB concentrations. Ex-situ study of catalyst surface after use and solid reaction products (precipitates) was performed by X-Ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The presence of cobalt hydroxide and oxyhydroxide was detected as major components on the catalyst surface after use and as precipitates in the supernatant solutions after washing. Cobalt borate, cobalt carbonate and oxycarbonate were also formed but in lesser amounts. These oxidized cobalt species were formed and further detached from the catalyst at the end of the reaction and/or during catalyst washing by decomposition of the unstable in-situ formed cobalt boride. Leaching of cobalt soluble species was negligible. Thin film mechanical detachment was also found but in a smaller extent. To study the influence of catalyst composition on deactivation processes, cycling experiments were performed with Co-B and Co-C catalysts, also prepared as thin films. We found that the deactivation mechanism proposed by us for the pure Co catalyst also occurred for a different pure Co (prepared at higher pressure) and the Co-B and Co-C samples in our experimental conditions.
Keywords: Hydrogen; Sodium borohydride; Co thin film catalyst; Deactivation; Cobalt hydroxide/oxyhydroxide;
Enhancement of photocatalytic performance with the use of noble-metal-decorated TiO2 nanocrystals as highly active catalysts for aerobic oxidation under visible-light irradiation by Yu Chen; Yannan Wang; Weizun Li; Qian Yang; Qidong Hou; Lianghuan Wei; Le Liu; Fang Huang; Meiting Ju (352-367).
Display OmittedThe use of noble metals loaded on semiconductor supports, through the absorption of visible light by metal nanoparticles, has opened new avenues for the improvement of catalytic performance under light irradiation. In this study, a series of different coinage metals such as gold, silver, platinum, and palladium loaded on TiO2 were prepared by photo-deposition and characterized by transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller analysis, UV–vis diffuse reflectance spectroscopy, photoluminescence emission, and X-ray photoelectron spectroscopy. The photocatalytic activity of M–TiO2 (M = Au, Ag, Pt, and Pd) samples was evaluated by the selective oxidation of benzyl alcohol under visible-light irradiation. In addition, the relationship between the light intensity, light wavelength, temperature of the reaction, and photocatalytic efficiency was investigated; the photocatalytic efficiency increased directly by increasing the light intensity or reaction temperature or by adjusting the irradiation wavelength in the most appropriate range. Particularly, Pt2–TiO2, with a Pt nanoparticle size ∼2 nm, created an Schottky barrier, so as to promote the electron transfer from platinum to titanium, which in turn promotes the aerobic oxidation of benzyl alcohol with an apparent quantum yield of 5.58% (at 400 nm). The mechanism of the oxidation process of benzyl alcohol over Pt2–TiO2 is also presented. In addition, platinum and palladium nanoparticles exhibited an even more profound improvement in catalytic performance at a high operating temperature (80 °C); these catalysts can be used as photo-thermocatalyst, which can more efficiently drive chemical conversion by coupling light and heat energy sources.
Keywords: Noble metal nanoparticles; Photocatalytic selective oxidation; Irradiation wavelength; Light intensity; Reaction temperature;
Efficiently photoelectrocatalyze CO2 to methanol using Ru(II)-pyridyl complex covalently bonded on TiO2 nanotube arrays by Jibo Liu; Huijie Shi; Qi Shen; Chenyan Guo; Guohua Zhao (368-378).
Display OmittedAiming at improving the efficiency of photoelectrocatalytic (PEC) CO2 conversion to methanol, a heterogeneous photoelectrocatalyst was prepared by covalently binding a Ru(II) metal-organic complex (Ru-Py) containing exposed pyridyl on the periodic TiO2 nanotube arrays (TNTAs). PEC characterization indicated that the Ru-Py/TNTAs photocathode exhibited excellent PEC CO2 reduction activity in aqueous solution. The initial CO2 reduction potential on Ru-Py/TNTAs photocathode reached −0.4 V (vs. NHE) under simulated solar irradiation. The cathodic photocurrent response of Ru-Py/TNTAs in CO2-satuarated aqueous solution was about 1.79 mAcm−2, which was 2.4 times that of TNTAs. It may be caused by the enhanced light absorption in the visible region originated from Ru-Py. Meanwhile, Ru-Py played an important role in accelerating the separation of photoinduced electron-hole pairs evidenced by the photoluminescence spectra. PEC CO2 reduction test showed that 84.8 μmol methanol was produced with 63.9% faraday efficiency, 62.6 turnover number (TON) and 45% selectivity at −0.9 V under 8 h irradiation. Furthermore, the non-covalent bonded system only produced 41.3 μmol methanol indicating that the carboxylic covalent linking displayed excellent electron transfer efficiency and methanolization performance. The mechanism investigation revealed that the exposed pyridyl provided the active sites in forming pyridiniumformate intermediates confirmed by the differential UV–vis absorption (ΔA) spectrum, which was of great significance in the efficient CO2 methanolization. The probable reaction pathway for catalytic CO2 reduction to methanol was also proposed combining the possible intermediates detected by gas chromatography mass spectrometry (GCMS).
Keywords: CO2 reduction; Methanol; Metal-organic complex; Covalent linking; Pyridiniumformate;
Antimony oxide hydrate (Sb2O5·3H2O) as a simple and high efficient photocatalyst for oxidation of benzene by Jing Chen; Zhangsen Chen; Xiaoyun Zhang; Xiaofang Li; Linhui Yu; Danzhen Li (379-385).
Display OmittedThe development of high efficient and inexpensive photocatalyst for oxidation of indoor gaseous benzene is a big challenge. In this paper, a simple compound containing only one metal element named antimony oxide hydrate (Sb2O5·3H2O) is prepared by a facile hydrolysis–oxidation method. The photocatalytic activity for oxidation of benzene over Sb2O5·3H2O is investigated for the first time. The conversion ratio and mineralization of benzene are 35.0% and 55% over Sb2O5·3H2O, which are 3.5 and 5.5 times higher than that of P25. Reactive oxygen species, including O2 • − and •OH, are detected by ESR experiments. The large amount of O2 • − and long lived •OH over antimony oxide hydrate is the main reason for its good photocatalytic activity, and it is also proved that both O2 • − and •OH are mainly origin from oxygen reduction. We believe that this energy saving, inexpensive and high efficient photocatalyst has potential industrial application value.
Keywords: Photocatalysis; Benzene; Photocatalytic oxidation; Antimonic acid; Antimony oxide hydrate;
Graphene-analogue h-BN coupled Bi-rich Bi4O5Br2 layered microspheres for enhanced visible-light photocatalytic activity and mechanism insight by Shanshan Ding; Danjun Mao; Shaogui Yang; Fei Wang; Lingjun Meng; Mengshu Han; Huan He; Cheng Sun; Bin Xu (386-399).
Display OmittedThe novel boron nitride coupled Bi-rich Bi4O5Br2 layered microspheres (h-BN/Bi4O5Br2-LMs) were successfully synthesized via a facile ionic liquid-in-water (IL/W) microemulsion-mediated route. The physical, chemical and optical properties of these heterojunction photocatalysts were thoroughly characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM) and UV–vis diffuse reflection spectroscopy (DRS). Their photocatalytic activities were primarily evaluated by degradation of 4-tert-butylphenol (PTBP), which found 1.0 wt% h-BN/Bi4O5Br2-LMs to be the best one. The photocurrent experiments showed that the photocurrent density of 1.0 wt% h-BN/Bi4O5Br2-LMs was four times higher than that of pure Bi4O5Br2-LMs due to enhanced charge transfer ability of the former. It revealed that the addition of h-BN was in favor of suppressing the photoinduced electron-hole pair recombination of Bi4O5Br2-LMs, so as to improve the photocatalytic activity of the composite. •O2 − and h+ were proved to be the main reactive species in the photocatalytic process by scavenger experiments and electron paramagnetic resonance (EPR) spectra. In addition, the photocatalytic mechanism of h-BN/Bi4O5Br2-LMs was further elaborated in this work. The probable degradation products were identified by GC–MS. The proposed conjugated addition and oxidation reactions were described to be the main pathways by combining the frontier electron density calculation and GC–MS results.
Keywords: Heterojunction photocatalyst; Boron nitride/Bi-rich Bi4O5Br2 layered microspheres; Microemulsion-mediated method; Photocatalytic mechanism; Degradation products;
Inorganic/whole-cell biohybrid photocatalyst for highly efficient hydrogen production from water by Yuki Honda; Motonori Watanabe; Hidehisa Hagiwara; Shintaro Ida; Tatsumi Ishihara (400-406).
Display OmittedTo obtain a clean hydrogen production system, we have developed an inorganic-bio hybrid photocatalyst system based on the combination of anatase TiO2, methylviologen (MV) as an electron mediator, and a whole-cell biocatalyst consisting of [FeFe]-hydrogenase and maturase gene-harboring recombinant Escherichia coli; however, the apparent quantum yield at 300 nm (AQY300) for hydrogen production was low (0.3%). The system consists of a two-step reaction: (1) photocatalytic MV reduction by TiO2, and (2) hydrogen production with reduced MV using a biocatalyst. The enhancement of step 1 under biocatalyst-friendly conditions was investigated in an attempt to further improve the reaction efficiency. Among the condition tested, the use of 100 mM Tris-HCl (pH 7), 150 mM NaCl, and 5% (v/v) glycerol with P-25 TiO2 especially enhanced the step 1 reaction by a 300-fold increase in the MV reduction rate compared with previously tested reaction condition (100 mM Tris-HCl (pH 7), 150 mM NaCl, 5% (v/v) glycerol, and 100 mM ascorbate with anatase TiO2). Under the enhanced step 1 reaction, AQY300 and AQY350 for photocatalytic MV reduction reached 60.8% and 52.2%, respectively. The enhanced step 1 reaction thus significantly improved the overall photocatalytic hydrogen productivity of the hybrid system and AQY300 and AQY350 reached 26.4% and 31.2%, respectively. The inorganic-whole-cell biohybrid system can therefore provide noble metal-free, efficient, and clean hydrogen production.
Keywords: [FeFe]-hydrogenase; Inorganic-bio hybrid; Photocatalysis; Water splitting; Whole-cell biocatalyst;
Ethylene production via catalytic dehydration of diluted bioethanol: A step towards an integrated biorefinery by Ilenia Rossetti; Matteo Compagnoni; Elisabetta Finocchio; Gianguido Ramis; Alessandro Di Michele; Yannick Millot; Stanislaw Dzwigaj (407-420).
Display OmittedAfter a preliminary thermodynamic investigation, proper operating conditions have been selected to maximise ethylene productivity by ethanol dehydration and limit side products such as coke and higher olefins or oxygenates. We focused on the possibility to operate with a diluted bioethanol solution (ca. 50 wt%), which represents a promising and convenient raw material, obtainable by simple flash concentration of the fermentation broth. Furthermore, water addition to the ethanol dehydration reactor may help preventing catalyst coking and diethyl ether formation, although affecting the thermodynamic products distribution. A proof of concept for an ethanol dehydration process using diluted ethanol is also provided through process simulation.Catalysts based on a BEA zeolite have been compared, characterised by different acidity imparted by dealumination treatments. Ni addition in variable loading helped suppressing undesired byproducts, difficult to separate from ethylene. For instance, no trace of diethyl ether nor acetaldehyde has been observed for the Ni-loaded samples under optimised working conditions.Catalyst characterisation by FT IR allowed correlating a high selectivity to ethylene with the acid sites nature of the catalyst, whereas the presence of extraframework Lewis acidic sites induced faster coke formation.Durability was finally checked on the most active and selective catalyst evidencing stable operation for 80 h-on-stream and without evidence of coke deposition, as determined after characterisation of the spent samples. A γ-Al2O3 catalyst has been tested as benchmark under the same conditions.
Keywords: Ethylene production; Ni catalysts; BEA zeolite; Bioethanol conversion to chemicals; Acid site;
Effects of microporous TiO2 support on the catalytic and structural properties of V2O5/microporous TiO2 for the selective catalytic reduction of NO by NH3 by Inhak Song; Seunghee Youn; Hwangho Lee; Seung Gwan Lee; Sung June Cho; Do Heui Kim (421-431).
Display OmittedSelective catalytic reduction (SCR) of NO by NH3 over vanadium-based catalyst is often accompanied with unwanted nitrous oxide (N2O) formation, which has 300 times higher global warming potential than CO2. In this work, VOx dispersed on microporous TiO2 catalysts calcined at various temperatures were applied to standard SCR reaction compared with VOx on commercial TiO2 ones. Both catalysts showed stable NOx reduction activity although they did completely different trend in N2O formation. Specifically, N2O was much less produced on VOx/microporous TiO2 catalysts regardless of calcination temperature with or without water in the reactant. Structural characterization of the catalysts using H2-TPR and Vanadium XANES revealed that the microporous TiO2 could suppress the formation of bulk-like V2O5 species, which are generally suggested as the main cause of N2O formation, in comparison of non-microporous commercial TiO2 support. Also, NH3-TPD and in situ DRIFTS studies showed that VOx on microporous TiO2 maintained strong Brønsted acidity so that it was capable of providing adsorbed NH3 species readily up to high temperature, which led to the stable DeNOx performance. We found that such two promoting effects seemed functionally analogous to those of tungsten oxide, which is conventionally used as a promoting material for the VOx/TiO2 catalyst. Our results demonstrated that vanadium oxides can be effectively stabilized up to high loading by structurally modifying TiO2 support, and also provided reasonable explanation about the promoting effects of microporous TiO2 support on the catalytic activity and structural properties of VOx/TiO2 catalyst.
Keywords: NH3-SCR; Vanadia; N2O formation; Microporous TiO2;
Steam catalytic cracking of heavy naphtha (C12) to high octane naphtha over B-MFI zeolite by Mohammed A. Sanhoob; Oki Muraza; Emad N. Shafei; Toshiyuki Yokoi; Ki-Hyouk Choi (432-443).
Display OmittedContinues consuming of fuel from fossil oil reservoirs due to the increase in energy demands encouraged scientists to use the pyrolysis of biomass in the production of clean energy. One of the most important product from the pyrolysis of biomass is dodecane. However, dodecane requires a further transformation in order to produce lighter hydrocarbons. Borosilicalite-1 (B-MFI) was synthesized with different mineralizer agents and utilized for steam catalytic cracking of dodecane. Furthermore, the amount of cooperative incorporation of boron to zeolitic framework contributes in adjusting the zeolitic acidity and consequently the amount of weak acid sites were observed to be proportional to the contents of boron. However, from pyridine-FTIR analysis, it was noticed that the acid site nature of borosilicalite-1 samples exhibited Brønsted acid site. Nevertheless, the presence of alkali fluoride as mineralizer agent enhanced the presence of boron in tetrahedral coordination system, which led to lower catalytic activity. While samples synthesized in the presence of alkali hydroxide were catalytically more active in steam catalytic cracking of dodecane due to its exhibit in trigonal coordination system. It was found that borosilicalite-1 was more stable when it was synthesized in the presence of sodium hydroxide as mineralizer agent rather than potassium hydroxide and the conversion was reached to 95% at 350 °C with space velocity of 4 h−1 when the Si/B ratio was 10.
Keywords: Biomass; Dodecane; Borosilicalite-1; Mineralizer agent; MFI;
Revisiting the mechanism of hexavalent chromium ion reduction: The parallel photodecomposition and photocatalytic reduction of chromate(VI) ester by Fei Xu; Richard D. Webster; Jinfan Chen; Timothy T.Y. Tan; Patrick H.-L. Sit; Wey Yang Teoh (444-453).
Display OmittedThe formation and homogeneous photodecomposition of chromate(VI) ester are often overlooked during the studies of photocatalytic reduction of hexavalent chromium, Cr(VI), in the presence of sacrificial electron donors such as methanol. When photoexcited (λ ≤ 525 nm), the chromate(VI) ester, formed by the spontaneous reaction of aqueous Cr(VI) with methanol, undergoes homogeneous stepwise decomposition to trivalent chromium, Cr(III). The addition of semiconductor photocatalysts, i.e., TiO2 and WO3, at relatively low concentrations (<0.5 g L−1) was detrimental to the overall rate of Cr(VI) reduction. This was traced to the occurrence of interfacial electron injection from chromate ester to the photocatalyst conduction band, that in turn interrupted inner sphere electron transfer, i.e., photodecomposition. Since it is an interfacial process, the extent of suppression of Cr(VI) reduction is more significant for highly adsorbing TiO2 than on weakly adsorbing WO3. At the same time, even though chromate ester adsorbs strongly on Al2O3, the interfacial electron injection to the insulator particle was unfavorable, and hence no suppression in Cr(VI) reduction was observed. When the TiO2 photocatalyst concentration was increased to 0.5 g L−1 and beyond, the photocatalytic reduction path became dominant. Further increase in the photocatalyst concentration saw the linear dependency in the apparent rate of Cr(VI) reduction, as expected for reaction in the non-mass diffusion and non-light scattering limited region. As followed by the electron paramagnetic spectroscopy, both the photodecomposition and photocatalytic reactions follow the stepwise reduction from Cr(VI) to Cr(V) and eventually to Cr(III). For non-photoexcited TiO2 (λ ≥ 420 nm), suppression in the rate of Cr(VI) reduction was observed at all concentrations tested. Importantly, the work showcases the parallel but non-independent effects of homogeneous photodecomposition of chromate(VI) ester and its photocatalytic reduction over semiconductor photocatalysts.
Keywords: Photocatalysis; Hexavalent chromium; Interfacial charge transfer; Density functional theory; Electron paramagnetic resonance;
Ni-Co layered double hydroxides cocatalyst for sustainable oxygen photosynthesis by Mingwen Zhang; Zhishan Luo; Min Zhou; Guigang Zhang; Khalid A. Alamry; Layla A. Taib; Abdullah M. Asiri; Xinchen Wang (454-461).
Display OmittedThe oxidation side of overall water splitting reaction, involving multiple electron transfer, O―H bond cleavage, and O―O bond formation, is a vital step to control the overall activities of water spitting. However, this process is usually restricted by the huge energy barrier and sluggish reaction kinetics. Recently, cobalt-based nanomaterials have been proved to be capable of decreasing the activation energy and accelerating the reaction kinetics. In principle, many factors will largely affect the activities, such as the loading contents, the size and structure of the cocatalysts. In order to achieve an overall enhancement of catalytic activities, it is reasonable to fabricate a tight and well matching junction that could efficiently promote the interface charge migration and separation. Herein, a high-performance water oxidation junction with layered structure was fabricated via in-situ growth of Ni-Co layered double hydroxides (LDHs) on graphitic carbon nitride nanosheets. Owing to the similarity of their layered stacking geometry, LDHs will strongly anchor on the surface of carbon nitride nanosheets, which could favor the photocatalytic water oxidation activities. As expected, the optimized binary catalysts showed remarkably enhanced activity for the photocatalytic water oxidation to release oxygen, which was 6.5 times higher than that of pure carbon nitride materials without loading the cocatalyst.
Keywords: Layered double hydroxides; Water oxidation cocatalysts; Carbon nitride nanosheets; Sustainable elements; Photocatalysis;
Promoted effect of alkalization on the catalytic performance of Rh/alk-Ti3C2X2 (X＝O, F) for the hydrodechlorination of chlorophenols in base-free aqueous medium by Mei Ming; Yanlin Ren; Min Hu; Yun Zhang; Ting Sun; Yuling Ma; Xiaojing Li; Weidong Jiang; Daojiang Gao; Jian Bi; Guangyin Fan (462-469).
Stable and recycled catalyst of Rh/alk-Ti3C2X2: The Rh/alk-Ti3C2X2 catalyst, prepared with small Rh NPs with relatively high dispersion, exhibited excellent catalytic activity and could be recycled at least five times for the hydrodechlorination of 4-chlorophenol under base-free conditions.Display OmittedExploring MXenes as supports for synthesis of highly efficient catalysts are extremely important for hydrodechlorination of chlorophenols because of the acute toxicity and strong potential bioaccumulation of chlorophenols. We reported a facile strategy to synthesize Rh nanoparticles deposited on 2D alk-Ti3C2X2 (X = O, F) (alk-Ti3C2X2 for short) MXene, which was prepared through the removal of the Al layers of Ti3AlC2 and post-treatment by alkalization. Modifying the Ti3C2X2 support by alkalization triggered the substitution of surface fluorine groups with surface oxygen species. The changes in the surface chemistry of alk-Ti3C2X2 effectively prevented particle aggregation to form well-dispersed Rh nanoparticles in small sizes with relative high metal dispersion, thereafter improving the hydrogen uptake capacity of the catalyst. Consequently, the Rh/alk-Ti3C2X2 catalyst significantly enhanced the catalytic performance for the HDC reaction, which could be assigned to the large number of active components from small Rh nanoparticles. This strategy provides a basis for investigating the use of MXenes as supports to synthesize well-defined metal nanoparticles in 2D layered structures for potential applications.
Keywords: MXenes; Rhodium; Alkalization; Hydrodechlorination; Base-free;
Atomic layer deposition-SiO2 layers protected PdCoNi nanoparticles supported on TiO2 nanopowders: Exceptionally stable nanocatalyst for the dehydrogenation of formic acid by Nurdan Caner; Ahmet Bulut; Mehmet Yurderi; Ilknur Efecan Ertas; Hilal Kivrak; Murat Kaya; Mehmet Zahmakiran (470-483).
Display OmittedTiO2 nanopowders supported trimetallic PdCoNi alloy nanoparticles were simply and reproducibly prepared by wet-impregnation followed by simultaneous reduction method, then to enhance their stability against to sintering and leaching atomic layer deposition (ALD) technique was utilized to grow SiO2 layers amongst these surface bound PdCoNi alloy nanoparticles (PdCoNi/TiO2-ALD-SiO2). These new nanomaterials are characterized by the combination of complimentary techniques and sum of their results exhibited that the formation of ALD-SiO2 layers protected well-dispersed and highly crystalline PdCoNi alloy nanoparticles (ca. 3.52 nm) supported on TiO2 nanopowders. The catalytic performance of the resulting PdCoNi/TiO2-ALD-SiO2 in terms of activity, selectivity and stability was investigated in the dehydrogenation of aqueous formic acid (HCOOH), which has recently been suggested as a promising hydrogen storage material with a 4.4 wt% hydrogen capacity, solution under mild conditions. The results collected from our systematic studies revealed that PdCoNi/TiO2-ALD-SiO2 nanomaterial can act as highly active and selective nanocatalyst in the formic acid dehydrogenation at room temperature by providing an initial turnover frequency (TOF) value of 207 mol H2/mol metal × h and >99% of dehydrogenation selectivity at almost complete conversion. More importantly, the catalytic reusability experiments separately carried out with PdCoNi/TiO2-ALD-SiO2 and PdCoNi/TiO2 nanocatalysts in the dehydrogenation of formic acid under more forcing conditions pointed out that PdCoNi/TiO2-ALD-SiO2 nanocatalyst displays unprecedented catalytic stability against to leaching and sintering throughout the reusability experiments it retains almost its inherent activity, selectivity and conversion even at 20th reuse, whereas analogous PdCoNi/TiO2 completely lost its catalytic performance.
Keywords: Atomic layer deposition; Nanocatalyst; Alloy; Formic acid; Dehydrogenation;
PANI/FeUiO-66 nanohybrids with enhanced visible-light promoted photocatalytic activity for the selectively aerobic oxidation of aromatic alcohols by Xueqing Xu; Ruxue Liu; Yuhan Cui; Xixi Liang; Cheng Lei; Shuangyan Meng; Yali Ma; Ziqiang Lei; Zhiwang Yang (484-494).
A PANI/FeUiO-66 nanohybrid was implemented as an efficient visible-light response photocatalysts for the photooxidation of the alcohols with superior conversions and selectivities. when the Fe doped onto the UiO-66, it could reduce the recombination rate of photoexcited charges. Besides, based on energy band matching between FeUiO-66 and PANI, the easily formed heterostructures from PANI and FeUiO-66 can efficiently enhance the separation of photogenerated carriers. Moreover, by virtue of unique advantage of the position of the CB and VB of FeUiO-66, alcohols could be selectively oxidized by the •O2 − and h+. Therefore, it is hoped that the MOF-conductive conjugated polymers nanocomposites could be used as efficient visible light driven photocatalysts for organic transformation with high selectivity under environment friendly conditions.Display OmittedMetal-organic frameworks (MOFs), a new class of porous crystalline materials, have attracted great interest as fascinating applications for eco-friendly photocatalysts. In this study, new hybrid MOFs, iron doped zirconium based metal-organic frameworks, FeUiO-66, were successfully synthesized by hydrothermal method firstly. Then the PANI/FeUiO-66 nanohybrids were fabricated through annealing process. The photocatalytic performances of the obtained PANI/FeUiO-66 nanohybrids were evaluated by selectively oxidation of various alcohol substrates using molecular oxygen as a benign oxidant. Boosting by synergistically multi-doped effect, the catalytic activity of the novel PANI/FeUiO-66 is remarkably higher than that of bare UiO-66 under visible light irradiation at ambient temperature. Further analyses revealed that the enhancement of photocatalytic activity originated from the two aspects. On one hand, when the Fe doped into the framework, valence fluctuation of Fe2+/Fe3+ could reduce the recombination rate of photoexcited carriers. On the other hand, based on energy band matching between FeUiO-66 and PANI, the easily formed heterostructures from PANI and FeUiO-66 can efficiently enhance the separation of photogenerated carriers. Furthermore, by virtue of unique advantage of the position of the CB and VB of FeUiO-66, alcohols could be selectively oxidized by the •O2 − and h+. Remarkably, it is expected that the MOF-conductive conjugated polymers nanohybrids could be used as efficient visible light driven photocatalysts for organic transformation with high selectivity under eco-friendly conditions.
Keywords: Photocatalysis; MOFs; PANI; FeUiO-66; Aerobic oxidation of alcohols;
Bio-based and environmental input for transfer hydrogenation using EcoNi(0) catalyst in isopropanol by V. Escande; C. Poullain; G. Clavé; E. Petit; N. Masquelez; P. Hesemann; C. Grison (495-503).
Display OmittedThe transfer hydrogenation of carbonyl compounds into alcohols with isopropanol has emerged as a green alternative to the use of hazardous reducing agents. Ni(0) nanoparticles have been described as an efficient catalyst for this reaction, while their classical preparation is still associated with a number of safety and environmental concerns. Here, we report a sustainable, ecological and straightforward preparation of a biosourced Ni(0) based material, by thermal decomposition of Ni(II) formate made from a Ni hyperaccumulating plant. The resulting catalyst, EcoNi(0), shows high catalytic activity and selectivity for the transfer hydrogenation of carbonyl compounds, including challenging aldehydes. The process seeks to be an incentive for the economic development of phytoextraction.
Keywords: Sustainable chemistry; Ecocatalysis; Bio-sourced catalyst; Reduction; Phytoextraction;
An effective strategy to improve dynamic and cyclic stability of HQC/TiO2 photocatalyst by introducing carbon quantum dots or iron ion via metal-complex by Dandan Ni; Qingkun Shang; Tongtong Guo; Xinyue Wang; Yongmei Wu; Hongyu Guan; Dan Wang; Min Zhang (504-512).
Display OmittedA novel photocatalyst, 8-hydroxy-Quinoline-7-carboxylic acid/TiO2 (HQC/TiO2) was synthesized and used to decompose phenol under visible light irradiation. It exhibited excellent photocatalytic activities, about 95.9% of phenol can be degraded after 2 h visible light illumination. However, the recycling efficiency is not very ideal. In order to improve its photostability during recycling process, we had adopted a novel and effective strategy for the introduction of carbon quantum dots or iron ions into the photocatalytic system. Two other novel catalysts, CQDs/HQC/TiO2 and Fe(HQC)3/TiO2 were prepared. After investigated the structure and morphology characteristics of HQC/TiO2, CQDs/HQC/TiO2 and Fe(HQC)3/TiO2 by analysis of X-ray diffraction, FTIR spectra, UV–vis absorption and diffuse reflectance spectra, X-ray photoelectron spectroscopy, transmission electron microscopic and photoelectrochemical properties, the possible and different photocatalytic mechanisms for these three photocatalysts were proposed. On the basis of this, the key factors affecting the dynamic and cyclic stability of HQC/TiO2 by introducing CQDs or Fe3+ ions via Fe-HQC complex were explored.
Keywords: Dynamic and cyclic stability; Carbon quantum dots; Interfacial interaction and electron transport; Photocatalysis under visible light;
Synergetic control of band gap and structural transformation for optimizing TiO2 photocatalysts by Heechae Choi; Sovann Khan; Junghyun Choi; Duong T.T. Dinh; Seung Yong Lee; Ungyu Paik; So-Hye Cho; Seungchul Kim (513-521).
Display OmittedImpurity doping and synthesizing polymorphic particles are the common strategies to improve activity of TiO2 photocatalyst by lowering the band gap and enhancing electron-hole separation rate. However, these two approaches have side effects. Doping of impurities make space charge region (SCR) thinner near the surface, which requires smaller sized particles than undoped TiO2 for the optimal performance. Polymorphic TiO2 particles, in which rutile and anatase phases coexist in a particle, are usually large due to energetic unstability of the rutile phase in a fine particle. For this contradiction that one needs small size while the other needs large size, two effects are not easy to be combined. In this study, we suggest a dual-doping strategy to solve the contradictory problem of SCR reduction by donor doping and inevitable size growth in polymorphic particles. We successfully dope W, a band gap narrower, into fine size of polymorphic particles by Sn-codoping, a promoter of the anatase-to-rutile transformation (ART), and demonstrate greatly improved photocatalytic activity. The accelerated ART by Sn-doping could keep the size of polymorph junctioned TiO2 small (∼10 nm) as lower temperature annealing become able to induce the ART. The concept of dual doping with a band gap narrower and an ART promoter provides a way to synthesize highly active photocatalysts by overcoming the drawback from shortened SCR length.
Keywords: Photocatalysis; Titanium dioxide; Polymorphic nanoparticles; Anatase-to-rutile transformation; W and Sn codoping;
A versatile cobalt catalyst for the reductive amination of carbonyl compounds with nitro compounds by transfer hydrogenation by Peng Zhou; Zehui Zhang; Liang Jiang; Changlin Yu; Kangle Lv; Jie Sun; Shuguo Wang (522-532).
Display OmittedOne-pot reductive amination of carbonyl compounds with nitro compounds has been reoprted for the first time by transfer hydrogenation with formic acid as the hydrogen donor over heterogeneous non-noble metal catalyst.Co nanoparticles embedded in mesoporous nitrogen-doped carbon (abbreviated as Co@CN-800) were prepared and found to be resistant to acid. The Co@CN-800 catalyst was found to be active and selective for the one-pot reductive amination of carbonyl compounds with nitro compounds by transfer hydrogenation with formic acid as the hydrogen donor, affording the corresponding secondary amines with excellent yields (89.6–99%). Both nitrogen atoms and Co nanoparticles were of great importance in the one-pot reductive amination over the Co@CN-800 catalyst by formic acid, and the protic N-H+ and hydridic Co-H− were proposed to be the active species for the transfer hydrogenation reactions. Furthermore, the Co@CN-800 catalyst was highly stable without loss of its activity.
Keywords: Non-noble heterogeneous catalyst; Nitro compounds; Hydrogenation; Transfer hydrogenation; Reductive coupling reaction;