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Applied Catalysis B, Environmental (v.108-109, #)
A study of the kinetic solvent isotope effect on the destruction of microcystin-LR and geosmin using TiO2 photocatalysis by Peter K.J. Robertson; Detlef W. Bahnemann; Linda A. Lawton; Edmund Bellu (pp. 1-5).
Display Omitted► Solvent isotope study of photocatalytic degradation of two cyanobacterial species. ► Results indicate photocatalytic process occurs at catalyst surface rather than bulk of solution. ► Scale of isotope effect dependent on photocatalyst employed. ► Rate determining step appears to be substrate degradation and not oxygen reduction.We have previously reported the effectiveness of TiO2 photocatalysis in the destruction of species generated by cyanobacteria, specifically geosmin and microcystin-LR. In this paper we report an investigation of factors which influence the rate of the toxin destruction at the catalyst surface. A primary kinetic solvent isotope effect of approximately 1.5 was observed when the destruction was performed in a heavy water solvent. This is in contrast to previous reports of a solvent isotope effect of approximately 3, however, these studies were undertaken with a different photocatalyst material. The solvent isotope effect therefore appears to be dependent on the photocatalyst material used. The results of the study support the theory that the photocatalytic decomposition occurs on the catalyst surface rather than in the bulk of the solution. Furthermore it appears that the rate determining step is not oxygen reduction as previously reported.
Keywords: Photocatalyst; TiO; 2; Microcystin; Geosmin; Heavy water; Drinking water; Kinetic solvent isotope effect
Hydrogen production from biomass gasification with Ni/MCM-41 catalysts: Influence of Ni content by Chunfei Wu; Leizhi Wang; Paul T. Williams; Jeffrey Shi; Jun Huang (pp. 6-13).
Display Omitted► The NiO particles of the prepared catalyst were located inside the pores of the MCM-41 at 5 or 10wt.% of Ni loading. ► A high dispersion of Ni was obtained for the prepared catalyst. ► Some NiO particles were formed outside the pores of the 20 or 40wt.% Ni/MCM-41 catalyst. ► Hydrogen and gas production were increased with the increase of Ni loading during the biomass gasification process. ► Less than 4wt.% of coke was deposited on the reacted Ni/MCM-41 catalyst.The steam pyrolysis-gasification of biomass, wood sawdust, was carried out with a Ni/MCM-41 catalyst for hydrogen production in a two-stage fixed bed reaction system. The wood sawdust was pyrolysed in the first reactor and the derived products were gasified in the second reactor. The synthesised MCM-41 mesoporous catalyst supports were impregnated with different Ni loadings (5, 10, 20 and 40wt.%), which were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). NiO particles were homogeneously dispersed inside the pores of 5, 10, and 20wt.% Ni/MCM-41 catalysts; however, more bulkly NiO particles (up to 200nm particle size) were detected outside the pores with an increase of the Ni loading up to 40wt.%. Gas production was increased from 40.7 to 62.8wt.%, hydrogen production was increased from 30.1 to 50.6vol.% of total gas composition when the Ni loading was increased from 5 to 40wt.% during the pyrolysis-gasification of wood sawdust. This work showed low coke deposition (from 0.5 to 4.0wt.%) with valuable bio-oil by-products using the Ni/MCM-41 catalyst. The highly efficient conversion of renewable biomass resource to hydrogen and bio-oil with very low coke deposition indicates that biomass gasification on Ni/MCM-41 catalysts via two-stage reaction is a promising method for the development of the biorefinery concept.
Keywords: Biomass; Pyrolysis; Gasification; Ni/MCM-41; Two-stage fixed bed reactor
Photocatalytic degradation of TCE in dry and wet air conditions with TiO2 porous thin films by S. Suárez; N. Arconada; Y. Castro; J.M. Coronado; R. Portela; A. Durán; B. Sánchez (pp. 14-21).
Display Omitted► Photocatalytic performance on TiO2 thin films for TCE abatement. ► Increase of the photocatalytic activity by effect of the pore generating agent. ► Influence of the relative humidity on the mineralization. ► Formation of COCl2 even at low water partial pressure.Porous TiO2-anatase thin films were prepared by the sol–gel route and used for the study of the influence of structural properties in their photocatalytic activity. Sols were prepared by using titanium isopropoxide with two types of modifier ligands, namely acetic acid and acetyl acetone, and pore generating agents such as polyethylene glycol, pluronic F-127 and polyethylene glycol hexadecyl ether (Brij 58). The photocatalytic activity for the degradation of trichloroethylene in air was evaluated under ultraviolet irradiation at different gas flows and water vapour contents. The photocatalytic activity depends on the nature of the pore generating agent which influences the TiO2 crystallite size and the textural properties of the final material. The samples obtained by using acetic acid as the modifier ligand and either Brij 58 or PEG as the pore generating agent exhibited the best photocatalytic behaviour even in the presence of high quantities of water vapour. The direct trichloroethylene oxidation pathway to CO2 is favoured at low water vapour contents, but an important generation of COCl2 is observed even at low water partial pressures.
Keywords: Photocatalysis; Trichloroethylene degradation; Gas phase; Phosgene; COCl; 2; Relative humidity; TiO; 2; thin films; Sol–gel; Pore generating agent; PEG; Brij 58; F-127; Porosity; Spectral ellipsometry; Environmental ellipsometric porosimetry (EEP)
Correlations between oxygen activation and methane oxidation over Pd/γ-Al2O3 catalysts prepared by nitrite method by Satu Ojala; Nicolas Bion; Alexandre Baylet; Mehrad Tarighi; Riitta L. Keiski; Daniel Duprez (pp. 22-31).
.Display Omitted► Pd prepared by nitrite-method is very active in methane oxidation and O2 activation. ► Reduction stage in preparation and reduction prior experiment enhance Pd activity. ► Easy Pd reducibility and Pd–alumina interactions have connection to good activity. ► Carbonates formed due to CO2 production in CH4 oxidation may enhance O2 activation.In this work the oxygen activation properties and methane oxidation activities of Pd/Al2O3 catalysts prepared by the nitrite-complex method are investigated. The effects of altering the preparation procedure and in-situ pre-treatments are considered. Based on the results, correlations between isotopic exchange and methane oxidation activities are drawn. Even if Pd/Al2O3 catalysts have typically a low activity in oxygen activation, it was found, that reductive in-situ pre-treatment of the catalyst significantly enhances the activity of oxygen activation studied by isotopic exchange and equilibration experiments. In addition, both equilibration and exchange take place on the pre-oxidized catalyst, whereas mainly equilibration occurs on the pre-reduced catalyst. The catalyst sample that was reduced prior to washing in the preparation stage showed to be most active in both cases, in isotopic oxygen exchange and in methane oxidation. The explanation to the enhanced activity is suggested to be originated from more easy reducibility of palladium.
Keywords: Isotopic exchange; Isotopic equilibration; Methane oxidation
Improvement of oxygen storage capacity using mesoporous ceria–zirconia solid solutions by Sara Abdollahzadeh-Ghom; Cyrus Zamani; Teresa Andreu; Mauro Epifani; J.R. Morante (pp. 32-38).
Display Omitted► Mesoporous ceria–zirconia with a high oxygen storage capacity is synthesized and characterized. ► Uniform nanoparticles with KIT-6 and SBA-15 are formed with a controlled pore size. ► A high OSC is received as compared to ceria (30 times higher than pure material). ► Formation of unsuitable tetragonal phase is observed for Zr contents above 20% which results in a plateau in OSC curve of the material.Mesoporous phases of ceria (CeO2) and ceria–zirconia solid solutions up to 50% of Zr have been synthesized using hard template method. The structures of the obtained metal oxides replicas correspond to the chosen structures of the KIT-6 and SBA-15 silica. This method allows obtaining materials with a uniform and homogenous porous size distribution as replica of the used nanotemplate. This structure facilitates the interaction with the gas molecules, their diffusivity inside the material and the porous size control. Obtained replicas were analysed using a variety of characterization techniques. TEM results reveal successful formation of the expected structures which were also supported by BET measurements. Replicas obtained applying SBA-15 and KIT-6 nanotemplates present similar behaviour although KIT-6 shows a slightly higher (about 5%) active surface with values in the range of 125m2/g after thermal annealing. XRD and Raman spectra confirm formation of solid solutions with cubic structure up to 20% of zirconium above which, formation of tetragonal phase was observed. Functionally, besides their high active surface, these ceria–zirconia solid solutions show significant improvement in their oxygen storage capacity (OSC). In comparison with pure mesoporous ceria, it has been found that due to the introduction of zirconium even for a few percentage of zirconium (5%) the OSC increases (more than 30 times) which is attributed to the presence of substitutional zirconium in the ceria lattice.
Keywords: Mesoporous; Ceria; Zirconia; KIT-6; SBA-15; Oxygen storage capacity; Hard template
Sintering-resistant and self-regenerative properties of Ag/SnO2 catalyst for soot oxidation by Ken-ichi Shimizu; Makoto Katagiri; Shigeo Satokawa; Atsushi Satsuma (pp. 39-46).
Ag/SnO2 as a highly sintering-resistant and active catalyst for soot oxidation is developed. Active Ag species have a strong interaction with SnO2 under reductive and oxidative environments at high-temperature, which results in a reversible regeneration of the active site structure.Display Omitted► Ag/SnO2 as highly sintering-resistant and active catalyst for soot oxidation. ► Ag on SnO2 did not markedly sinter at 1000°C (higher than the melting point of Ag) and reduction/oxidation treatment at 800°C. ► Reversible structural change between Ag nanoparticle and Ag3Sn enables the self-regenerative property.Key factors controlling the thermal and redox-cycle stability of Ag/SnO2 catalyst were investigated to establish the design concept of “self-regenerative” soot oxidation catalysts. The effect of thermal aging (in air at 1000°C) on the soot oxidation activity was tested for Ag catalysts supported on SnO2, CeO2, ZrO2, TiO2, and MgO and SnO2-supported Cu, Pd, Rh, Ru, and Pt. Ag/SnO2 is found to be the most effective catalysts in terms of both activity and thermal stability. XRD and EXAFS results showed that particle growth of metal or metal oxide by the thermal aging was the main reason of the decreased soot oxidation activity, and the supported Ag species on Ag/SnO2 showed high sintering-resistance owing to the Ag–O–Sn bonds at metal–support interface. The effect of redox aging at 800°C on the soot oxidation activity and structure of Ag/SnO2 was also studied. H2-reduction of Ag/SnO2 lead to the formation of the large (20nm) particles of Ag3Sn, which were then redispersed by the reoxidation treatment to small Ag nanoparticles. This self-regenerative property lead to no catalyst deactivation of Ag/SnO2 after successive redox treatments. It is concluded that the strong chemical interaction between silver and tin species (metallic and oxidic Sn) under both reductive and oxidative environments at high-temperature enables the design of highly sintering resistant Ag-based oxidation catalysts.
Keywords: Soot oxidation; Sintering; Silver; Tin oxide
Visible light photocatalytic activity enhancement for water purification in Cu(II)-grafted WO3 thin films grown by photoreaction of nanoparticles by Tomohiko Nakajima; Takuya Kitamura; Tetsuo Tsuchiya (pp. 47-53).
Display Omitted► WO3 nanoparticles with 5–30nm size are obtained by ball milling as catalyst precursors. ► KrF laser irradiation of the films enhances anomalous crystallite growth. ► Laser-induced photothermal and photochemical effects are the key factors for crystal growth. ► Very high photocatalytic dye degradation activity in the film prepared by KrF laser irradiation.We have developed a simple process for improving the visible light photocatalytic activity in Cu(II)-grafted WO3 thin films, called ‘the photoreaction of nanoparticles’ (PRNP). The films prepared by PRNP showed an enhanced photodegradation rate for an organic dye. Glass substrates were coated with WO3 nanoparticles (5–30nm) obtained by wet ball milling, and a post-treatment of either conventional heating or PRNP using KrF laser irradiation was carried out. Compared with the conventional heat treatment at 500°C, PRNP significantly enhanced surface crystallite growth; pulsed photothermal gradient heating and photochemical stimulation increased the formation of new bonds between nanoparticles. The crystallite size near the surface of the WO3 film after 7500 pulses of laser irradiation increased to 70nm, while it was largely-unchanged in the sample prepared by heat treatment at 500°C. The photocatalytic dye degradation under visible light irradiation was measured for the samples after Cu(II)-grafting, and showed that the degradation rate of the sample prepared by the PRNP process was 2.8-fold higher than that of the sample prepared by heating at 500°C. We propose that the improved surface crystallinity of WO3 thin films after the PRNP process stimulates the photoexcited electron/hole transfer at the film surface, resulting in the enhancement of photocatalytic activity.
Keywords: WO; 3; Photocatalyst; Nanoparticles; Laser treatment; Water purification
Catalytic hydrothermal hydrodenitrogenation of pyridine by Peigao Duan; Phillip E. Savage (pp. 54-60).
Display Omitted► 5% Pt/γ-Al2O3 catalyzes the hydrothermal HDN of pyridine to produce hydrocarbons. ► Nitrogen in pyridine can be effectively removed in SCW in the presence of a Pt/γ-Al2O3 catalyst and high-pressure H2. ► The main HDN products of pyridine are n-butane and n-pentane.We herein report on the hydrothermal catalytic conversion of pyridine to hydrocarbons. The catalytic activity of several supported noble metal (5wt%) catalysts (Pt/C, Pd/C, Ru/C and Rh/C, sulfided Pt/C, and Pt/γ-Al2O3), a traditional hydrodenitrogenation (HDN) catalyst (sulfided CoMo/γ-Al2O3), a transition metal carbide (Mo2C) and sulfide (MoS2), and a noble metal oxide (PtO2) toward the HDN of pyridine in a hydrothermal reaction medium between 250 and 400°C was determined. The Pt/γ-Al2O3 catalyst proved to be the most active for hydrothermal HDN of pyridine, and we report the effects of batch holding time, reaction temperature, catalyst loading, initial hydrogen pressure, and water density on the Pt/γ-Al2O3-catalyzed HDN of pyridine in supercritical water. The latter two process variables had the greatest influence on the product yields and distribution. Conditions were identified that lead to essentially 100% conversion of pyridine to N-free hydrocarbons. The catalyst shows some modest loss in activity upon being reused. An HDN reaction network for pyridine under hydrothermal conditions was proposed. The main HDN products are n-butane and n-pentane. Nitrogen was removed as ammonia.
Keywords: Hydrothermal; Hydrodenitrogenation; Pyridine; Pt/γ-Al; 2; O; 3; Supercritical water
Liquid-phase degradation of polyethylene (PE) over MFI zeolites with mesopores: Effects of the structure of PE and the characteristics of mesopores by Jae Youl Lee; Se Min Park; Shyamal Kumar Saha; Sung June Cho; Gon Seo (pp. 61-71).
MFI-sda with mesopores in a MFI framework exhibited enhanced catalytic activity in the degradation of LLDPE even with a low level of catalyst loading (0.05g/10g LLDPE) at 380°C because of its wide external surface and large amount of strong acid sites.Display Omitted► Four kinds of MFI-meso zeolites with different porous and acidic properties were prepared and characterized. ► The constitution of mesopores with MFI topology was confirmed by the processing of TEM images. ► The introduction of mesopores into MFI zeolite enhanced its catalytic activity in the degradation of HDPE and LLDPE.Four kinds of MFI-meso zeolites with both micro- and mesopores were prepared, characterized, and their catalytic activities were evaluated in the liquid-phase degradation of high-density, low-density, and linear low-density polyethylene (HDPE, LDPE, and LLDPE) in order to discuss their catalytic performance in relation to their porous characteristics and acidity. MFI-syn that was synthesized from partially dissolved MFI zeolite and MFI-sda that was prepared by using a special structure directing agent exhibited highly ordered mesopores with strong acidity and achieved high conversions, about 95%, even with small catalyst loadings (HDPE/catalyst=20g/0.05g) at 380°C. However, MFI-oxy prepared from an oxyacid-added mixture exhibited a poor catalytic activity because of its low acidity and small pore volume. MFI-alk prepared by an alkali treatment exhibited irregular mesopores and medium conversions. MFI-meso zeolites were especially suitable for the degradation of HDPE and LLDPE, which required a high external surface for the initial degradation of polyethylene and a rapid mass transfer, resulting in a higher catalytic activity. The enhancement of catalytic activity in the degradation of LDPE by the introduction of mesopores was relatively small because of its rapid initial degradation.
Keywords: Degradation; Polyethylene; MFI zeolite; Mesopore; Acidity
Purification of hydrogen from carbon monoxide for fuel cell application over modified mesoporous CuO–CeO2 catalysts by Jing Li; Yuxi Han; Yihan Zhu; Renxian Zhou (pp. 72-80).
Display Omitted► The introduction of Mn and Fe plays a beneficial role in extending the low-temperature catalytic activity of CuO–CeO2 catalysts. ► The introduction of Cr and Co leads to a negative effect. ► Mn and Fe doping enhances the interaction between copper and ceria and facilitates the formation of solid solution. ► The introduced cobalt ions substitute for copper ions in ceria lattice. ► The introduction of Cr remarkably weakens the interaction between copper and ceria.Selective oxidation of CO in H2-rich streams was carried out over a series of CuO–CeO2 catalysts doped by different transition metals (Mn, Fe, Ni, Ti, Co and Cr). The effect of the dopants on the structure and catalytic properties of CuO–CeO2 catalysts was investigated by N2 adsorption/desorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), Raman spectra and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques. The results show that the addition of Mn and Fe plays a beneficial role in extending the low-temperature catalytic activity of CuO–CeO2 catalysts, whereas the introduction of Cr and Co leads to a negative effect on the catalytic activity and resistance against CO2 and H2O. The superior catalytic performance of CuO–CeO2 catalysts with Mn and Fe doping originates from the enhanced interaction between copper and ceria, owing to the formation of more Cu+ and oxygen vacancies in the solid solution framework. While the poor catalytic activity of the Co doped counterpart is mainly ascribed to the substitution of introduced cobalt ions for copper ions in ceria lattice, resulting in the segregation of copper ions from the ceria lattice and the consequent aggregation of copper species on the ceria surface. The doping of Cr into CuO–CeO2 structure remarkably weakens the interaction between copper and ceria, which decreases the reducibility of copper species and inhibits the formation of Cu+. It accounts for the lowest catalytic activity.
Keywords: CuO–CeO; 2; Transition metals; CO selective oxidation; Cu; +; Oxygen vacancies
Preparation of ordered mesoporous carbons containing well-dispersed and highly alloying Pt–Co bimetallic nanoparticles toward methanol-resistant oxygen reduction reaction by Shou-Heng Liu; Feng-Sheng Zheng; Jyun-Ren Wu (pp. 81-89).
Display Omitted► A novel route has been developed to synthesize well-dispersed and alloying PtCo nanoparticles supported on nanostructure carbons. ► Electrochemical measurements of oxygen reduction demonstrated that synthesized materials possess high catalytic activity and surpassing methanol tolerance compared to common commercial catalysts. ► This may be attributed to the dispersion and unique nanostructure of highly alloyed PtCo nanoparticles supported on synthesized catalysts.A simple route is described for the synthesis of well-dispersed and highly alloying PtCo bifunctional nanoparticles supported on ordered mesoporous carbons (Pt100− xCo x/OMC) by the simultaneous pyrolysis of carbon and metal precursors in a mesoporous silica as the hard template. A variety of different spectroscopic and analytical techniques was used to thoroughly characterize the Pt100− xCo x/OMC samples. By X-ray diffraction, N2 adsorption/desorption isotherms and transmission electron microscopy, it was found that Pt100− xCo x/OMC possessed well-dispersed Pt/PtCo nanoparticles (2–3nm) supported on high surface area (∼1000m2g−1) and regular pore channels (∼2.8nm). Among Pt100− xCo x/OMC catalysts, the Pt50Co50/OMC was found to have superior electrocatalytic activity and the tolerance to methanol crossover during oxygen reduction reaction as compared to typical commercial electrocatalysts. This may be attributed to the dispersion and unique nanostructure of highly alloyed PtCo nanoparticles supported on Pt50Co50/OMC evidenced by X-ray absorption spectroscopy.
Keywords: PtCo alloy; Ordered mesoporous carbons; Oxygen reduction reaction; Methanol tolerance; XANES/EXAFS
Ag/MCM-41 as a highly efficient mesostructured catalyst for the chemoselective synthesis of methyl glycolate and ethylene glycol by Anyuan Yin; Chao Wen; Wei-Lin Dai; Kangnian Fan (pp. 90-99).
High yield of methyl glycolate (MG, >99%) and ethylene glycol (EG, >99%) could be obtained via the gas-phase hydrogenation of dimethyl oxalate over Ag/MCM-41 catalyst synthesized via ammonia-evaporating deposition-precipitation method under the optimized reaction conditions.Display Omitted► A highly active and selective Ag/MCM-41 catalyst was prepared for the first time. ► This catalyst was applied in the gas-phase continuous hydrogenation of DMO to MG and EG. ► The DMO conversion and the selectivity to MG and EG can be up to 100%, and 99%. ► The best Ag/MCM-41 catalyst obtained after calcined at 673K with 10wt.% loading. ► Different pretreatment atmosphere leads to different catalytic performance for this catalyst.A novel highly efficient heterogeneous Ag/MCM-41 catalyst was prepared by ammonia-evaporation deposition-precipitation method and displayed outstanding methyl glycolate (MG) selectivity (up to 99%) and ethylene glycol (EG) selectivity (up to 99%) in the chemoselective gas-phase hydrogenation of dimethyloxalate (DMO). Systematic characterizations have been carried out to elucidate the bulk and surface physicochemical properties of the catalysts. It is shown that the silver loading, the calcination temperature, the surface hydroxyl group amount and the pretreatment atmosphere all have great influences on the catalytic performance of DMO hydrogenation reaction. The best catalytic performance could be achieved over the Ag/MCM-41 catalyst with 10wt.% silver loading after calcined at 673K. Much higher catalytic activity could be obtained via the MCM-41 supported silver catalyst with large amount of surface hydroxyl groups. The argon pretreated Ag/MCM-41 catalyst with less subsurface oxygen species exhibited much higher DMO conversion and MG selectivity compared with H2 and air pretreated samples. Under the optimized reaction conditions, 99% yield of MG and EG could be obtained over the optimized Ag/MCM-41 catalyst.
Keywords: Ag/MCM-41; Dimethyl oxalate; Ethylene glycol; Methyl glycolate; Hydrogenation
Novel visible light-induced g-C3N4/Bi2WO6 composite photocatalysts for efficient degradation of methyl orange by Lei Ge; Changcun Han; Jing Liu (pp. 100-107).
Novel visible light induced g-C3N4/Bi2WO6 heterojunction photocatalysts were synthesized by introducing polymeric g-C3N4 for the first time. The g-C3N4/Bi2WO6 samples showed the high efficiency for the photodegradation of methyl orange. The enhancement of photocatalytic performance of the g-C3N4/Bi2WO6 composite materials is attributed to the synergic effect between polymeric g-C3N4 and Bi2WO6 and effectively separation of photo-generated electron–hole pairs.Display Omitted► Novel g-C3N4/Bi2WO6 heterojunction photocatalyst were prepared for the first time. ► The g-C3N4/Bi2WO6 showed remarkably enhanced photocatalytic activity. ► The arrangement and interfaces between g-C3N4 and Bi2WO6 were revealed by HRTEM. ► Photodegraded mechanism was proposed based on energy band positions. ► The mechanism was confirmed by PL spectra and photocatalytic results.Novel visible light-induced g-C3N4/Bi2WO6 composite photocatalysts were synthesized by introducing polymeric g-C3N4. The obtained g-C3N4/Bi2WO6 products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, ultraviolet–visible diffuse reflection spectroscopy (DRS), and photoluminescence spectroscopy. The DRS results revealed that the g-C3N4/Bi2WO6 samples had a red shift and strong absorption in the visible light region. The photocatalytic oxidation ability of the novel photocatalyst was evaluated using methyl orange as a target pollutant. The photocatalysts exhibited a significantly enhanced photocatalytic performance in degrading methyl orange. The optimal g-C3N4 content for the photocatalytic activity of the heterojunction structures was determined. The synergic effect between g-C3N4 and Bi2WO6 was found to lead to an improved photo-generated carrier separation. Consequently, the photocatalytic performance of the g-C3N4/Bi2WO6 composites under visible light irradiation ( λ>420nm) was enhanced. The possible photocatalytic mechanism of the composites was proposed to guide the further improvement of their photocatalytic activity.
Keywords: g-C; 3; N; 4; Bi; 2; WO; 6; Photocatalysis; Functional; Semiconductors
Comparative study of visible-light-driven photocatalytic mechanisms of dye decolorization and bacterial disinfection by B–Ni-codoped TiO2 microspheres: The role of different reactive species by Wanjun Wang; Lizhi Zhang; Taicheng An; Guiying Li; Ho-Yin Yip; Po-Keung Wong (pp. 108-116).
For photocatalytic decolorization of dye, the reaction mainly occurs on the catalyst surface with the aid of surface-bounded reactive species (h+,OHs andO2−), while bacteria can be long-range inactivated without the direct contact with the photocatalysts.Display Omitted► Bacterial disinfection does not require direct contact with BNT catalyst, while dye decolorization requires. ► H2O2 plays the major role in bacterial disinfection. ► Coupling of bothOHb andOHs produces H2O2 in the valence band. ►O2− directly involves bacterial disinfection. ► A versatile research strategy is developed to study the photocatalytic mechanisms.The controversy of mechanism still exists over whether photocatalytic decontamination proceeds via photon-generated h+, e−,OH,O2− or H2O2. This study aims to investigate the roles of these reactive charges and oxidative species in the photocatalytic dye decolorization and bacterial disinfection processes in the presence of a visible-light-driven (VLD) photocatalyst, B–Ni-codoped TiO2 microsphere, by employing various scavengers in the photocatalytic system and utilizing a novel partition system. Significant differences between VLD photocatalytic dye decolorization and bacterial disinfection are found. For photocatalytic dye decolorization, the reaction mainly occurs on the photocatalyst surface with the aid of surface-bounded reactive species (h+,OHs andO2−), while bacterial cell can be inactivated by diffusing reactive oxidative species such asOHb and H2O2 without the direct contact with the photocatalyst. The diffusing H2O2 plays the most important role in the photocatalytic disinfection, which can be produced both by the coupling ofOHb in bulk solution andOHs on the surface of photocatalyst at the valence band. Furthermore, theO2−, which is detected by using the electron spin resonance technique, is found to have direct function for the photocatalytic disinfection process. This study establishes a facile and versatile research methodology to investigate the VLD photocatalytic mechanism in different photocatalytic system.
Keywords: Photocatalysis; Dye decolorization; Bacterial disinfection; Partition system; Hydrogen peroxide
Ce0.67Fe0.33O2− δ and Ce0.65Fe0.33Pt0.02O2− δ: New water gas shift (WGS) catalysts by N. Mahadevaiah; Preetam Singh; Bhaskar Devu Mukri; Sanjit K. Parida; M.S. Hegde (pp. 117-126).
.Display Omitted► Ce0.65Fe0.33Pt0.02O2− δ and Ce0.67Fe0.33O2− δ catalysts are synthesized by a sonochemical method. ► Ce0.67Fe0.33O2− δ acts as a catalyst for CO oxidation and WGS reactions at moderate temperatures. ► Ce0.65Fe0.33Pt0.02O2− δ is an excellent catalyst for CO oxidation and WGS reactions at lower temperatures. ► Rate of CO conversion with the Pt free catalysts is lower, compared to Pt substituted catalysts in WGS reactions. ► No deactivation of the catalysts observed even long time start-up/shut-down operations.Ce0.65Fe0.33Pt0.02O2− δ and Ce0.67Fe0.33O2− δ have been synthesized by a new low temperature sonochemical method using diethylenetriamine as a complexing agent. Due to the substitution of Fe and Pt ions in CeO2, lattice oxygen is activated in Ce0.67Fe0.33O2− δ and Ce0.65Fe0.33Pt0.02O2− δ. Hydrogen uptake studies show strong reduction peaks at 125°C in Ce0.65Fe0.33Pt0.02O2− δ against a hydrogen uptake peak at 420°C in Ce0.67Fe0.33O2− δ. Fe substituted ceria, Ce0.67Fe0.33O2− δ itself acts as a catalyst for CO oxidation and water gas shift (WGS) reactions at moderate temperatures. The rate of CO conversion in WGS with Pt free Ce0.67Fe0.33O2− δ is 2.8μmolg−1s−1 at 450°C and with Pt substituted Ce0.65Fe0.33Pt0.02O2− δ is 4.05μmolg−1s−1 at 275°C. Due to the synergistic interaction of the Pt ion with Ce and Fe ions in Ce0.65Fe0.33Pt0.02O2− δ, the catalyst showed much higher activity for CO oxidation and WGS reactions compared to Ce0.67Fe0.33O2− δ. A reverse WGS reaction does not occur over Ce0.65Fe0.33Pt0.02O2− δ. The catalyst also does not deactivate even when operated for a long time. Nearly 100% conversion of CO to CO2 with 100% H2 selectivity is observed in WGS reactions even up to 550°C.
Keywords: WGS reaction; Oxygen storage capacity; Ce; 1−; x; Fe; x; O; 2−; δ; Ce; 1−; x; Fe; x; Pt; y; O; 2−; δ; WGS catalysts
Room-light-induced indoor air purification using an efficient Pt/N-TiO2 photocatalyst by Hongqi Sun; Ruh Ullah; Siewhui Chong; Hua Ming Ang; Moses O. Tadé; Shaobin Wang (pp. 127-133).
Display Omitted► Pt/N-TiO2 synthesised by a sol–gel method shows strong visible response.► Pt/N-TiO2 can degrade various VOCs at high rate at visible light.► Pt/N-TiO2 exhibits high activity of toluene degradation using room light.A conceptual air purifier harvesting fluorescent room lights was tested in this study. Visible photocatalysis was applied to facilitate the degradation of volatile organic compounds (VOCs) on a highly efficient visible light photocatalyst, Pt/N-TiO2 synthesised via a sol–gel process. The as-prepared photocatalyst was characterised by many techniques, such as XRD, XPS, UV–vis DRS, N2 adsorption and SEM, etc. XPS spectra revealed that platinum was at a chemical state of 2+, while nitrogen existed as NO x species. The unique chemical compositions made the photocatalyst respond to visible light with a band gap of 2.69eV, and present a broad absorption shoulder extended further into infrared region. The photocatalytic activities under irradiations of λ>387, 430 and 490nm were evaluated by photodegradation of phenol solutions. Under UV–vis light, the Pt/N-TiO2 exhibited 5.5 times higher activity than Degussa P25. Various gaseous pollutants were degraded by employing the Pt/N-TiO2 in a batch reactor. The capability of photodegradation of VOCs under room lights was also proven by the decomposition of gaseous toluene in a continuous reactor using fluorescent lamps (6×10W). The mechanism of the enhanced activity in degradation of VOCs and potential application were discussed.
Keywords: Visible light photocatalysis; Pt/N-TiO; 2; VOCs; Indoor air quality; Gas-phase
Attempts at an in situ Raman study of ceria/zirconia catalysts in PM combustion by James A. Sullivan; Petrica Dulgheru; Idriss Atribak; Agustín Bueno-López; Avelina García-García (pp. 134-139).
Display Omitted► Ce xZr1− xO2 samples fluoresce at high temperatures when probed using Raman spectroscopy. ► F2g/T2g peak reversibly moves to lower energy at high temperature. ► PM decreases intensity of Raman bands. ► High temperature treatment of Ce0.8Zr0.2O2/PM in He forms a Ce3+–CO adduct.Ce xZr1− xO2 catalysts with various Ce/Zr contents were studied using Raman spectroscopy under different gaseous atmospheres, at different temperatures and in the presence of a model soot. Catalysts with high concentrations of Zr fluoresced at elevated temperatures making analysis of their spectra impossible. This effect became even more pronounced at higher temperatures. CeO2 and solid solutions with relatively low concentrations of Zr showed a red shift and a decrease in intensity of the characteristic F2g peak at high temperatures under different atmospheres. The magnitude of the latter effect was higher under reducing atmospheres. These changes are reversible upon cooling, showing that they relate to a lattice expansion effect rather than any major chemical change to the material. In the presence of the model soot the Raman spectra of all materials was much decreased due to the absorption of the incident and scattered radiation by the soot particles. The presence of soot does not change the relative intensities or positions of the peaks in the spectra of the solid solutions. Evidence is shown for the production of a Ce3+–CO species following interaction between the soot and the surface at high temperature in an inert atmosphere.
Keywords: Ce; x; Zr; 1−; x; O; 2; PM combustion; In situ; Raman spectroscopy
Selection of oxygen reduction catalysts for rechargeable lithium–air batteries—Metal or oxide? by H. Cheng; K. Scott (pp. 140-151).
Display Omitted► Carbon-supported Pd and PdO as model electrocatalysts. ► Catalysts for oxygen reduction in rechargeable Li–air batteries. ► Model catalysts compare with Pt/C, Ru/C, RuO2/C and MnO2/C. ► Oxides are better cathode catalysts than their metal counterparts. ► Changes in property and structure affect the catalyst activity and stability.Carbon-supported Pd and PdO nanocatalysts were synthesised using either chemical reduction or thermal synthesis procedures and were used as model metal and oxide catalysts for oxygen reduction in rechargeable lithium–air batteries. The Pd metal catalyst showed excellent initial performance, e.g. a discharge capacity of 855mAh (gsolids)−1. However, the PdO catalyst displayed superior capacity retention to the Pd catalyst, producing a discharge capacity of 336mAh (gsolids)−1 after 10 cycles, i.e. the capacity retention was 6% per cycle. The activity and stability of Pd metal and oxide catalysts were found to be closely related to their intrinsic catalytic properties and structural changes during charge/discharge cycles in Li–air batteries. The implication of such a difference is discussed. Model Pd/C and PdO/C catalysts were compared with other widely used carbon-supported metal and oxide catalysts, including Pt/C, Ru/C, RuO2/C and MnO2/C.
Keywords: Rechargeable lithium–air battery; Palladium nanocatalysts; Palladium oxide nanocatalysts; Air cathode; Discharge capacity; Cycle ability
Effect of preparation of Pd and Pd–Pt catalysts from acid leached silica–alumina on their activity in HDS of thiophene and benzothiophene by Zdeněk Vít; Hana Kmentová; Luděk Kaluža; Daniela Gulková; Marta Boaro (pp. 152-160).
.Display Omitted► Extraction of part of alumina from mesoporous silica–alumina (MSA) by HNO3 increased the Brønsted acidity and surface area of MSA support. ► Both properties improved the HDS activities of Pd/MSA catalysts. ► Promotional effects over bimetallic Pd–Pt/MSA catalyst were observed in HDS of thiophene and benzothiophene.Mesoporous silica–alumina (MSA) modified by post-synthesis acid leaching was studied as a support for Pd and Pd–Pt catalysts. Activity of catalysts was evaluated in hydrodesulfurization (HDS) of model compounds (thiophene and benzothiophene). The leaching decreased the Al2O3 content of MSA from 52 to 9wt.%. This treatment mainly removed the non-acidic extra-framework Aloct species, exposed the Brønsted acidic sites and increased the BET surface area by 50%. The higher acidity and surface area improved the activities of Pd catalysts in HDS of thiophene and benzothiophene. Pd(OAc)2 deposited on the leached MSA gave the best monometallic Pd catalyst. Two bimetallic Pd–Pt catalysts were prepared by co-impregnation of the leached MSA with Pd(OAc)2+Pt(NH3)4(OH)2 and Pd(OAc)2+H2PtCl6. The bimetallic catalyst prepared from Pt(NH3)4(OH)2 showed significant promotional effect and exhibited the highest activity in HDS of thiophene and benzothiophene.
Keywords: Hydrodesulfurization; Silica–alumina; Acid leaching; Pd catalyst; Pd–Pt catalyst
Niobium-containing MCM-41 silica catalysts for biodiesel production by Cristina García-Sancho; Ramón Moreno-Tost; Josefa M. Mérida-Robles; José Santamaría-González; Antonio Jiménez-López; Pedro Maireles-Torres (pp. 161-167).
Niobium-containing MCM-41silica catalysts are very active in the methanolysis of sunflower oil at 200°C, even in the presence of an acidity of 1.1wt% and 0.2wt% water, without leaching.Display Omitted► Nb2O5 containing mesoporous silica is active for the acid-catalyzed biodiesel production. ► The catalysts can be reutilized, without leaching of the active phase. ► They catalyze the methanolysis of triglycerides, even in the presence of water and FFA.This research focuses on the synthesis and characterization of mesoporous niobosilicate molecular sieves and their catalytic activity in biodiesel production by transesterification of sunflower oil with methanol. Catalysts were prepared by two procedures: impregnation of a MCM-41 silica with different amounts of niobium oxalate and subsequent calcination, and structural incorporation of Nb into a MCM-41 silica during the synthesis step. Characterization techniques such as XRD, XPS, TEM, NH3-TPD and N2 sorption have been employed to characterize the synthesized catalysts. The biodiesel yield increases with the catalyst acidity, attaining a value of 95% with a 7.5wt% of a MCM-41 silica impregnated with a 8% of Nb2O5, at 200°C, after 4h of reaction and a methanol/oil molar ratio of 12. The potential of this family of catalysts to treat low-grade oils has been demonstrated by increasing the acidity of the sunflower oil by adding oleic acid (1.1wt%) and water (0.2wt%) to the reaction mixture, since the biodiesel yield is maintained close to 80%. Moreover, the catalyst reutilization has been demonstrated during five catalytic runs by employing a low-grade oil, with no leaching of the active phase.
Keywords: Niobium oxide; Mesoporous silica; Biodiesel; Transesterification; Acid catalysis
Solar light assisted photodegradation of phenol with hydrogen peroxide over iron-doped titania catalysts: Role of iron leached/readsorbed species by C. Adán; J. Carbajo; A. Bahamonde; I. Oller; S. Malato; A. Martínez-Arias (pp. 168-176).
Display Omitted► Unusually high phenol solar photodegradation activity is observed over iron-doped catalyst with high iron loading. ► Iron leaching/readsorption observed during the reaction indicates a mechanism of surface iron complexes. ► Iron becomes fully readsorbed on the catalyst surface during the course of the reaction, thus facilitating products separation.Nanostructured iron-doped TiO2 catalysts with anatase structure and two different iron contents (0.7 and 3.5wt.%) have been prepared by a combined sol–gel/microemulsion method and examined with respect to their behaviour for photocatalytic degradation of aqueous phenol with H2O2 under solar light. The activity results are compared with those obtained for similarly prepared undoped systems as well as Degussa P25 reference catalyst and have been complemented with structural/morphological and electronic characterization analyses achieved by XRD, TEM, Raman, SBET, UV–vis DRS and XPS techniques. In contrast to typically observed results, the highest photoactivity is obtained for the catalyst with highest iron loading while that with 0.7% Fe displays lower photoactivity than undoped samples. Such unusual behaviour has been attributed to the contribution of new photoactive iron complexes generated on the surface of the catalyst as a consequence of iron leaching and readsorption processes taking place during the course of phenol photodegradation process.
Keywords: Solar light; Photocatalysis; Iron leaching; Phenol photooxidation; TiO; 2; H; 2; O; 2
Carbon dioxide reforming of methane over ordered mesoporous NiO–MgO–Al2O3 composite oxides by Leilei Xu; Huanling Song; Lingjun Chou (pp. 177-190).
Display Omitted► Ordered mesoporous NiO-MgO-Al2O3 composite oxides with various Ni and Mg content were facilely synthesized via one-pot evaporation induced self-assembly strategy.► These materials were employed as the catalysts for dry reforming and behaved excellent catalytic activities and long stability.► Outstanding textural properties of the mesoporous materials and the “confinement effect” of the mesostructure contributed to distinguished catalytic performances.► The role of the MgO basic modifier was detailedly investigated.► Characteristics of the coke over the mesoporous catalyst were carefully studied.Ordered mesoporous NiO–MgO–Al2O3 composite oxides with various Ni and Mg content were facilely synthesized via one pot evaporation induced self-assembly (EISA) strategy. These mesoporous materials with large specific surface areas, big pore volumes, uniform pore sizes and superior thermal stability were investigated as the catalysts for the carbon dioxide reforming of methane reaction. These materials performed high catalytic activity as well as long stability. The improved catalytic performances were suggested to be closely associated with both the amount of “accessible” active centers for the reactants owing to their advantageous structural properties and the stabilized Ni nanoparticles by mesoporous framework matrix due to the “confinement effect” of the mesopores. Besides, the role of the MgO basic modifier was also studied. It was observed that only moderate amount of the Mg containing (2M%) could greatly promote the catalytic performances. The stabilized Ni nanoparticles as well as doped MgO had reinforced capacity of resistance to coke, accounting for no deactivation after 100h long-term stability test at 700°C. Therefore, the ordered mesoporous NiO–MgO–Al2O3 composite oxides promised a series of novel and stable catalyst candidates for carbon dioxide reforming of methane reaction.
Keywords: Ordered mesopore; NiO–MgO–Al; 2; O; 3; Carbon dioxide reforming; Methane