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Applied Catalysis B, Environmental (v.106, #1-2)
Bi2WO6 micro/nano-structures: Synthesis, modifications and visible-light-driven photocatalytic applications by Lisha Zhang; Huanli Wang; Zhigang Chen; Po Keung Wong; Jianshe Liu (pp. 1-13).
Display Omitted► Bi2WO6 has attracted much attention as one of newly developed visible-light-driven photocatalysts. ► We summarized the design, preparation and/or growth mechanism of Bi2WO6 based micro/nano-structures with diverse shapes and components. ► These Bi2WO6 based micro/nano-structures exhibited structure/component-dependent visible-light-driven photocatalytic activities on both the degradation of the organic pollutant and the disinfection of the bacteria.Currently, the photocatalytic reactions occurring under solar illumination have attracted worldwide attentions due to a tremendous set of environmental problems. Taking the sunlight into account, it is indispensable to develop highly effective visible-light-driven photocatalysts. Bi2WO6 is one of newly developed visible-light-driven photocatalysts, and its photocatalytic performance is seriously dependent on its structure, morphology and components. This article features recent research progress in the preparation and growth mechanism of Bi2WO6 micro/nano-structures, including nanoplates, nanoparticles, superstructures and thin films. In addition, the advances in the doped Bi2WO6 and Bi2WO6 based composites have also been overviewed. These Bi2WO6 based micro/nano-structures exhibit different photocatalytic performances on the degradation of the organic pollutant as well as the disinfection of the bacteria, and the effects of their structures and components on photocatalytic activities are also compared.
Keywords: Bi; 2; WO; 6; Micro/nano-structures; Synthesis; Modifications; Photocatalysis
Highly dispersed uniformly sized Pt nanoparticles on mesoporous Al-SBA-15 by solid state impregnation by Ana K. Medina-Mendoza; María A. Cortés-Jácome; Jose A. Toledo-Antonio; Carlos Angeles-Chávez; Esteban López-Salinas; Ignacio Cuauhtémoc-López; María C. Barrera; Jose Escobar; Juan Navarrete; Isaías Hernández (pp. 14-25).
Display Omitted► 1 nm Pt nanoparticles are formed by a solid impregnation of Pt(acac)2 on Al-SBA-15 ► A near sublimation point, 180̊C, heat-treatment is used to diffuse Pt(acac)2 onto SBA ► 6 times more edge/flat Pt sites are attained in comparison with a wet impregnation ► Pt/Al-SBA-15 is twice active in naphthalene hydrogenation than by wet impregnationHighly dispersed Pt nanoparticles on modified mesoporous Al-SBA-15 were obtained by a solid state impregnation (SSI) methodology, which consisted of a physical mixture of Al-SBA-15 support with a given amount of Pt(acac)2 in order to have 1wt.% of Pt on the final solid. The solid mixture was ground vigorously and annealed at 180°C (e.g. the sublimation point of Pt(acac)2) for 0.5h and then at 400°C in inert atmosphere, to decompose the organic ligand. The materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) by applying high angle annular dark field (HAADF) technique, nitrogen physisorption, pyridine adsorption by infrared spectroscopy (FTIR), X-ray photoelectronic spectroscopy (XPS) and FTIR of CO adsorption. Catalytic activity of Pt nanoparticles was evaluated in naphthalene hydrogenation (HYD) as test reaction. The results were compared with those obtained on Pt nanoparticles dispersed on Al-SBA-15 by wet impregnation (WI) method. Both SSI and WI methods produce significant differences in the population of flat and edge sites on the Pt nanoparticles with dimensions around 1.0nm. However, Pt nanoparticles obtained by SSI showed higher activity upon naphthalene HYD than those obtained by WI method, which was explained by the higher density of edge sites measured by FTIR of CO adsorption.
Keywords: Pt nanoparticles; Al-SBA-15; Solid state impregnation; Chemical grafting; Naphthalene hydrogenation
In situ XAS study on the mechanism of reactive adsorption desulfurization of oil product over Ni/ZnO by Lichun Huang; Guofu Wang; Zhangfeng Qin; Mei Dong; Mingxian Du; Hui Ge; Xuekuan Li; Yidong Zhao; Jing Zhang; Tiandou Hu; Jianguo Wang (pp. 26-38).
Display Omitted► In situ XAS was used to study the desulfurization of model oil containing dibenzothiophene (DBT) over Ni/ZnO.► In nitrogen, the desulfurization over Ni/ZnO is achieved through physical and chemical adsorption.► In hydrogen, the desulfurization turns to be a reactive adsorption process.► Hydrogen facilitates the decomposition of DBT on active Ni species, the formation of NiS x, and thereafter the transfer of sulfur to ZnO.► Metallic Ni as the active nickel species is preserved until most of ZnO is converted to ZnS.Reactive adsorption desulfurization (RADS) of a model oil n-nonane containing dibenzothiophene (DBT) was conducted over a Ni/ZnO adsorbent; the evolution of Ni/ZnO adsorbent structure during desulfurization was monitored by in situ X-ray absorption spectroscopy (XAS). The reaction mechanism under different atmospheres and the role of hydrogen in the desulfurization were investigated. The results indicated that the desulfurization processes under nitrogen and hydrogen are different in the reaction mechanism. In nitrogen, the desulfurization over Ni/ZnO is achieved through physical and chemical adsorption; a severe decrease in the desulfurization activity of Ni/ZnO is observed with the time on stream and the desulfurization capacity is very low. In hydrogen, the desulfurization turns to be a reactive adsorption process and Ni/ZnO exhibits a high desulfurization activity and capacity. Hydrogen plays an important role in the RADS; it facilitates the decomposition of DBT on active Ni species, the formation of Ni3S2, and thereafter the transfer of sulfur to ZnO. Metallic Ni as the active nickel species is preserved until most of ZnO is converted to ZnS. On the basis of these observations, a possible sulfur transfer mechanism for the RADS is then proposed.
Keywords: In situ XAS; Ni/ZnO; Reactive adsorption desulfurization; Dibenzothiophene; Sulfur transfer
TiO2 modified with both phosphate and platinum and its photocatalytic activities by Jungwon Kim; Wonyong Choi (pp. 39-45).
Display Omitted► P-TiO2/Pt showed higher photocatalytic activity than any of bare TiO2, P-TiO2, and Pt/TiO2. ► The high activity of P-TiO2/Pt is ascribed to the synergic action of two surface species and the enhanced production of OH radicals. ► P-TiO2/Pt minimized the production of toxic intermediate (2,4-dichlorophenol) during the photocatalytic degradation of 2,4-D. ► Synergic activity of P-TiO2/Pt was stable in a wide range of pH.A new hybrid modification method of TiO2 photocatalyst was developed and investigated. TiO2 modified with both phosphates and platinum nanoparticles on its surface (P-TiO2/Pt) was prepared by a simple two-step method using phosphoric acid (as phosphate source) and chloroplatinic acid (as platinum source). The coexistence of phosphate and platinum on the surface of TiO2 was confirmed by X-ray photoelectron spectroscopy and transmission electron micrography. P-TiO2/Pt showed a significantly higher photocatalytic activity than any of bare TiO2, P-TiO2, and Pt/TiO2 for the degradation of phenolic compounds (4-chlorophenol; bisphenol A; 2,4-dichlorophenoxyacetic acid (2,4-D)). In particular, P-TiO2/Pt minimized the production of toxic intermediate (2,4-dichlorophenol) during the photocatalytic degradation of 2,4-D. In accordance with the higher photocatalytic activities of P-TiO2/Pt, both the production of OH radicals and the photocurrent collection in the suspension were markedly enhanced upon the simultaneous platinization and phosphation of TiO2. The two surface species acted synergically to enhance the photocatalytic activity. The surface phosphation that should replace the surface hydroxyl groups on TiO2 favors the formation of unbound OH radicals instead of surface-bound OH radicals while the surface platinization accelerates the electron transfer with retarding the charge recombination. The phosphation of TiO2 was stable over a wide range of pH due to the strong chemical bonding of phosphate on TiO2 whereas the surface fluorination of TiO2, which can be similarly compared with the phosphation in its photocatalytic effect, is active only at acidic pH. P-TiO2/Pt showed a higher photocatalytic activity than Pt/TiO2 for the degradation of 2,4-D even at pH 11, under which condition the effect of surface fluorination of Pt/TiO2 completely disappeared.
Keywords: Titanium dioxide; Surface phosphation; Surface platinization; Photocatalytic degradation; Water treatment
Synthesis of MWCNT/MnO2 and their application for simultaneous oxidation of arsenite and sorption of arsenate by Tawfik A. Saleh; Shilpi Agarwal; Vinod K. Gupta (pp. 46-53).
Display Omitted► The composite of MWCNT/MnO2 was successfully synthesized. ► It combines the oxidation properties of MnO2 with adsorption features of MWCNTs. ► It shows high efficiency for removal of As(III) and As(V). ► The desorption process was successfully conducted.It is well known that arsenite [As(III)] is less effectively removed than arsenate [As(V)] by most treatment technologies. Thus, pre-oxidation of As(III) to As(V) is required prior to adsorption. Here, the oxidation properties of manganese oxides with adsorption features of multiwall carbon nanotubes (MWCNTs) have been combined in a composite of MWCNT/MnO2. The composite was characterized by Fourier transform infrared absorption spectroscopy (FTIR), field emission scanning electron microscope (FESEM), and energy dispersive X-ray (EDX) and X-ray diffraction (XRD). In batch culture experiments, MWCNTs and the MWCNT/MnO2 composite were examined for As(III) and As(V). The results reveal that MnO2 in the composite plays a key role in enhancing As(III) removal and As(III) removal is not as effective as As(V) removal for MWCNTs. The retention of arsenite and arsenate is slightly pH dependent. The reported composite can be regenerated as it was confirmed by SEM and EDX analysis. The study could be considered as a model of preparation and investigation of a multifunctional material that can be used in wastewater treatment for removal of arsenic.
Keywords: Carbon nanotubes/manganese oxide composite; Adsorption; Oxidation; Arsenic
Enhanced H2 formation by electrochemical promotion in a single chamber steam electrolysis cell by A. Caravaca; A. de Lucas-Consuegra; C. Molina-Mora; J.L. Valverde; F. Dorado (pp. 54-62).
.Display Omitted► A new single chamber solid electrolyte cell has been proposed for the production of H2. ► It has been studied under (CH4, H2O and O2) at mild temperature (600°C). ► It allows to combine catalysis (NEMCA) and electrocatalysis (steam electrolysis). ► Both processes can be coupled for the production of H2 with high efficiencies. ► The NEMCA effect can be assisted by the steam electrolysis for the production of H2.This study reports for the first time the possibility of coupling the phenomenon of electrochemical promotion and the steam electrolysis process for the simultaneous production of H2 in a single chamber solid electrolyte cell (Pt-YSZ/YSZ/Au) (working/solid electrolyte/counter). The system has been studied under methane partial oxidation, steam electrolysis and methane autothermal reforming conditions with application of different currents at 600°C. The highest H2 production rates were achieved under the last composition (autothermal reforming) and the application of negative currents over the Pt catalyst-working electrode. Thus, under those conditions, an additional increase in the H2 production rate was observed (apart from the H2 coming from the electrocatalytic processes), which was attributed to an intrinsic NEMCA effect in the simultaneous steam reforming of methane on the same Pt catalyst-working electrode. Hence, the novel configuration used in this work could have significant importance for the production of H2 with higher efficiencies at mild temperature by integrating the non-faradic enhanced catalytic processes (NEMCA in steam reforming) and electrocatalytic processes (steam electrolysis) in a single chamber configuration.
Keywords: Electrochemical promotion; NEMCA effect; H; 2; production; Steam electrolysis; Solid electrolyte cell
Photocatalytic reduction of bromate at C60 modified Bi2MoO6 under visible light irradiation by Xu Zhao; Huijuan Liu; Yuanli Shen; Jiuhui Qu (pp. 63-68).
The photocatalytic activity of the prepared Bi2MoO6 nanoparticles and C60 modified Bi2MoO6 in the reduction of bromate ions were evaluated under visible light irradiation. The obtained results indicated that bromate ions can be reduced by Bi2MoO6 nanoparticles and the reduction rate of bromate ions was increased by modifying C60. The deposited C60 molecules facilitated the separation of photogenerated electron–hole pairs, and enhance the photocatalytic activity of the Bi2MoO6 nanoparticles towards the reduction of bromate ions.Display Omitted► Bromate ions can be reduced by Bi2MoO6 nanoparticles via photocatalytic process under visible light irradiation. ► Modification of Bi2MoO6 nanoparticles by C60 increases the reduction rate of bromate ions via photocatalytic process. ► The deposited C60 molecules facilitated the separation of photogenerated electron–hole pairs, and enhanced the photocatalytic activity of the Bi2MoO6 nanoparticles towards the reduction of bromate ions.In the current work, Bi2MoO6 nanoparticles were prepared via hydrothermal method and obtained Bi2MoO6 nanoparticles were modified by C60. The photocatalytic activity of the prepared Bi2MoO6 nanoparticles and C60 modified Bi2MoO6 in the reduction of bromate ions were evaluated under visible light irradiation. It is observed that bromate ions can be reduced by Bi2MoO6 nanoparticles and the reduction rate of bromate ions was increased by the C60 modification. Based on the analysis of photoluminescence spectra and electrochemical impedance spectroscopy of the Bi2MoO6 and C60 modified Bi2MoO6, it is concluded that separation of photogenerated electron–hole pairs is enhanced via the modification of C60 molecules onto Bi2MoO6. Thus, the photocatalytic activity of the Bi2MoO6 nanoparticles towards the reduction of bromate ions was enhanced. The effect of loading amount of C60 on Bi2MoO6 nanoparticles on the bromate reduction was investigated. And, the reduction rate of bromate decreased with the solution pH value, which was discussed based on the electrostatic interaction. Effect of cations and anions on the reduction of bromate was investigated. The photogenerated electrons can be consumed by NO3−, which resulted in the decrease of BrO3− reduction. The photocatalytic reduction of bromate decreased with the addition of K2S2O8, which indicated that electrons played a dominant role in the reduction of bromate.
Keywords: C; 60; Bromate; Bi; 2; MoO; 6; Visible light; Photocatalysis
Highly active and stable CdS–TiO2 visible photocatalyst prepared by in situ sulfurization under supercritical conditions by Yuning Huo; Xiaolei Yang; Jian Zhu; Hexing Li (pp. 69-75).
Display Omitted► CdS–TiO2 photocatalyst is prepared by in situ sulfurization under supercritical conditions. ► CdS–TiO2 displays strong interaction between CdS and TiO2. ► High visible photoactivity is due to enhanced photosensitizing effect of CdS and inhibition of photoelectron-hole recombination. ► CdS–TiO2 exhibits long lifetime owing to the inhibition of photo-corrosion and leaching of CdS.A novel porous CdS–TiO2 photocatalyst with large surface area and high crystallization degree was synthesized by in situ sulfurization of doped TiO2 under supercritical conditions. The CdS acted as a photosensitizing agent to activate TiO2 in visible light area, while the TiO2 acted as an electron acceptor to separate the photo-induced electrons from holes in the CdS. Under visible light irradiation, the as-prepared CdS–TiO2 exhibited high activity in photocatalytic degradation of 4-chlorophenol (4-CP) owing to the high surface area, the well dispersed CdS nanocrystals, and especially the strong interaction between CdS and TiO2 which greatly enhanced the photosensitizing effect of CdS and also effectively inhibited the recombination between photo-induced electrons and holes. Meanwhile, the CdS–TiO2 also displayed strong durability since the strong interaction between CdS and TiO2 could efficiently protect the CdS from photo-corrosion and leaching off.
Keywords: Supercritical treatment; CdS–TiO; 2; visible-light photocatalyst; Photosensitization; CdS–TiO; 2; interaction; Degradation of 4-chlorphenol
Gram-scale production of graphene oxide–TiO2 nanorod composites: Towards high-activity photocatalytic materials by Jincheng Liu; Lei Liu; Hongwei Bai; Yinjie Wang; Darren D. Sun (pp. 76-82).
Display Omitted► High-quality graphene oxide–TiO2 nanorod composites (GO–TiO2 NRCs) were produced though a two-phase assembling method to produce on gram scale. ► The prepared GO–TiO2 NRCs had high photocatalytic activity in the photodegradation of C. I. Acid Orange 7 and the photocatalytic disinfection of Escherichia coli. ► The comparative study shows that TiO2 nanorods have better photocatalytic activity than TiO2 nanoparticles no matter whether they are anchored to GO sheets or not.Here we present a simple two-phase assembling method to produce high-quality graphene oxide–TiO2 nanorod composites (GO–TiO2 NRCs) on gram scale. TiO2 nanorods dispersed in toluene are synthesized from a facile two-phase hydrothermal method. The effective attachment of TiO2 nanorods on the whole GO sheets at the water–toluene interface is confirmed by Transmission Electron Microscope (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The as-synthesized TiO2 nanorods show a slightly higher efficiency in the photocatalytic degradation of C. I. Acid Orange 7 (AO 7) irradiated under UV light ( λ=254nm) and higher antibacterial activity under simulated sunlight than that of TiO2 nanoparticles with the same diameter. After combined with graphene oxide (GO), the GO–TiO2 NRCs show much higher photocatalytic activities than that of TiO2 nanorods alone and the GO–TiO2 nanoparticle composites (GO–TiO2 NPCs). The ratio of TiO2 and GO has no evident effect on the photocatalytic activity of GO–TiO2 NRCs when all the TiO2 nanorods are anchored on the GO sheets. The higher photocatalytic activity of GO–TiO2 NRCs is ascribed to the anti-charge recombination and the more (101) facets. Considering the superior photocatalytic activity of GO–TiO2 NRCs and the fact that they can been easily mass-produced, we expect this material may find important applications in environmental engineering and other fields.
Keywords: Graphene oxide; TiO; 2; Nanorod; Composites; Gram-scale; Two-phase
Glycerol liquid phase conversion over monometallic and bimetallic catalysts: Effect of metal, support type and reaction temperatures by A. Iriondo; J.F. Cambra; V.L. Barrio; M.B. Guemez; P.L. Arias; M.C. Sanchez-Sanchez; R.M. Navarro; J.L.G. Fierro (pp. 83-93).
.Display Omitted► Conversion was due to the formation of intermediate liquid oxygenated hydrocarbons at different temperatures. ► Among the liquid oxygenated hydrocarbons, 1,2-propylene glycol was the main product. ► Bimetallic catalysts showed good catalytic activity related with low dispersion of metallic active sites, Pt–Ni alloy formation and H2 spill-over. ► La2O3 addition improved the H2 yield by increasing Ni0 dispersion in Ni/γ-AM catalyst and surface exposure of Ni in PtNi/γ-AM catalyst. ► Ni catalysts deactivation observed was due to oxidation by water.Glycerol liquid conversion under catalytic aqueous steam reforming conditions was studied. For this purpose monometallic Ni and Pt and bimetallic PtNi catalysts supported on γ-Al2O3 and La2O3-modified γ-Al2O3 were employed. Activity measurements indicated that among the tested catalysts, the PtNi catalysts were, in general, the most active, whereas the Ni catalysts suffered from increasing deactivation as the temperature increased. In addition, glycerol conversion was mainly due to the production of intermediate oxygenated hydrocarbons at the reaction conditions investigated. In general, the presence of La2O3 improved this catalytic behaviour toward lighter gaseous products. The characterisation results, together with the activity results, suggested that the high activity of the PtNi catalysts can be associated with limited metal dispersion, the formation of metal Pt–Ni alloy and the spill-over phenomenon. The last two effects hindered carbon deposition. Furthermore, the deactivation of the Ni catalysts was also associated with the oxidation of metallic Ni phases in the presence of adsorbed H2O.
Keywords: Glycerol; Liquid; Reforming; Monometallic; Bimetallic
Acid–base properties of niobium-zirconium mixed oxide catalysts for glycerol dehydration by calorimetric and catalytic investigation by P. Lauriol-Garbey; G. Postole; S. Loridant; A. Auroux; V. Belliere-Baca; P. Rey; J.M.M. Millet (pp. 94-102).
Display Omitted► Zr and Nb mixed oxides are selective catalysts for dehydration of glycerol to acrolein in gas phase. ► Characterization of used catalysts showed that active sites are weak acid Brønsted sites. ► Linear relationship between weak acidic site number and rate of glycerol conversion was evidenced. ► Deactivation of catalysts with time on stream was related to the formation of cyclic molecules. ► Cyclic molecules are formed by reaction of acrolein with hydroxyacetone decomposition products.The acid–base properties of fresh and used niobium-zirconium mixed oxide catalysts, used for the dehydration of glycerol to acrolein, have been characterized by various techniques. These techniques include ammonia thermo-programmed desorption (TPD), infrared spectroscopy of absorbed pyridine, and adsorption microcalorimetry of ammonia and sulfur dioxide. Relationships between the catalytic properties and the acid–base properties of fresh catalysts have been investigated. The most efficient catalysts were shown to be those for which the zirconia support had a better niobium oxide species covering, but no specific relationship could be established between the acid–base, and the selectivity to acrolein. Characterization of the used catalysts showed that the acidic properties of the catalysts had changed considerably with the time spent on stream. No further strong acid sites, and only weak or very weak acid sites were detected. A linear relationship between the total quantity of remaining acidic sites and the rate of glycerol conversion was determined, taking into account an intrinsic activity of the stronger sites, which is more than ten times that of the weaker ones. The deactivation of the catalysts as a function of time on stream has been related to the formation of cyclic molecules, produced by the reaction of acrolein with by-products resulting from the decomposition of hydroxyacetone and also possibly acrolein and glycerol.
Keywords: Glycerol; Acrolein; Dehydration; Acid catalysis; Nb; 2; O; 5; -ZrO; 2; mixed oxide; Deactivation; Adsorption microcalorimetry
Suppression of the oxygen storage and release kinetics in Ce0.5Zr0.5O2 induced by P, Ca and Zn chemical poisoning by S.Y. Christou; M.C. Álvarez-Galván; J.L.G. Fierro; A.M. Efstathiou (pp. 103-113).
Effects of P, P–Ca and P–Zn deposition on the surface of Ce0.5Zr0.5O2 solid solution followed by calcination at 850°C on the surface and bulk oxygen diffusion kinetics and OSC quantity.Display Omitted► P (4.5wt%) deposition on Ce0.5Zr0.5O2 solid solution reduces significantly OSC. ► P–Zn co-deposition on Ce0.5Zr0.5O2 gives higher OSC than P deposition alone. ► P deposition on Ce0.5Zr0.5O2 followed by calcination at 850°C forms CePO4. ► CePO4 locks the Ce4+/Ce3+ redox couple and increases Eb for bulk O2− diffusion. ► P–Ca and P–Zn deposition on Ce0.5Zr0.5O2 strongly inhibits surface O n− diffusion.The present investigation concerns for the first time the understanding of the individual and combined effects of phosphorous with calcium or zinc deposited on a Ce0.5Zr0.5O2 solid followed by calcination in 20%O2/He at 850°C, on the kinetics of oxygen storage and release of the thus derived contaminated Ce0.5Zr0.5O2 solids. Towards this aim, physicochemical and redox properties of Ce0.5Zr0.5O2, P/Ce0.5Zr0.5O2, P–Ca/Ce0.5Zr0.5O2 and P–Zn/Ce0.5Zr0.5O2 solids were investigated by means of BET, XRD, SEM, XPS, TPR, OSC and TPIE techniques. P, Ca or Zn deposition on Ce0.5Zr0.5O2 solid was found to result in a drastic decrease in the population of reactive oxygen species present on the surface and within the subsurface/bulk region of the solid. The latter is attributed to the formation of cerium and calcium phosphates in the subsurface region of the solid, as well as to the formation of zinc oxide on the surface of the solid, clogging pores lower than 10nm in size as revealed by BJH pores size distribution measurements. Another reason for the severe reduction in the OSC (up to 70%) of contaminated by phosphorous Ce0.5Zr0.5O2 solid is the rearrangement of its surface composition resulting in the lowering of the Ce/Zr surface ratio. The latter is linked to the lowering of the concentration of reactive oxygen associated with the strength of Ce–O–Zr bonding. The incorporation of P within the subsurface region of Ce0.5Zr0.5O2 crystals and its reaction with the solid producing CePO4 causes the formation of a significant amount of Ce3+ which is very difficult to get re-oxidised, and locks the Ce(III)/Ce(IV) redox couple. Phosphorus incorporation within the subsurface/bulk of Ce0.5Zr0.5O2 solid oxide particles was found to significantly increase the activation energy of bulk oxygen diffusion from 126.5 to ∼169.0kJmol−1, while the concurrent deposition of Ca or Zn along with P was found to strongly suppress surface oxygen diffusion.
Keywords: TWC deactivation; Ceria–zirconia; Chemical poisoning; OSC; Oxygen isotopic exchange; TPIE
Promotion of activation of CH4 by H2S in oxidation of sour gas over sulfur tolerant SOFC anode catalysts by Adrien L. Vincent; Jing-Li Luo; Karl T. Chuang; Alan R. Sanger (pp. 114-122).
Display Omitted► H2S promotes methane activation on LST. ► The methane/H2S electrocatalytic oxidation selectivity depends on applied voltage. ► The fuel mixture methane H2S, provides a very high power density compared to the respective single gases. ► The major components of a mechanism are proposed.Hydrogen sulfide, usually considered to be an anode catalyst poison, strongly promotes methane oxidation over sulfur resistant catalysts. The role of H2S in oxidation of sour CH4 feed over a sulfur resistant SOFC anode catalyst at 850°C has been determined through thermodynamic and experimental studies. The anode material was an intimately mixed 50/50 mass ratio composite of La0.4Sr0.6TiO3− δ and YSZ. The power density improved dramatically from 2mWcm−2 with pure CH4 as fuel to more than 450mWcm−2 for CH4 containing 20% H2S. However, H2S was not the only fuel converted, and its interaction with CH4 was the key factor in enhancement of performance. The anode effluent gas mixture included H2S, SO2, H2 and CS2 consistent with thermodynamic predictions. The role of H2S in the CH4 oxidation mechanism was determined, and showed that CH4 and H2S must be considered together as a fuel and not as two separate fuels. The types of electrochemical reactions that occurred in the fuel cell were strongly dependent on potential.
Keywords: SOFC; H; 2; S; Methane; Titanate; Anode catalyst
Kinetic study of glycerol oxidation network over Pt–Bi/C catalyst by Wenbin Hu; Brian Lowry; Arvind Varma (pp. 123-132).
The kinetics of glycerol oxidation network over Pt–Bi/C catalyst was investigated systematically by performing studies for five progressively enlarging sub-networks. The obtained insights provide suggestions for the development of superior catalysts and the obtained kinetic parameters will be used to develop a continuous-flow reactor model for process design and optimization of DHA yield.Display Omitted► Glycerol oxidation network involves 10 steps and 9 species. ► Kinetic study was performed individually for 5 progressively enlarging subnetworks. ► All kinetic parameters associated with the 10 steps were determined. ► Tartronic acid has strong adsorption on Pt active sites. ► A 4-step simplified network represents the complex reaction network well.Identifying new uses for glycerol, a waste of biodiesel production from transesterification of vegetable oils, is of great current interest. Towards this end, catalytic oxidation of glycerol to produce the high-value chemical dihydroxyacetone (DHA) is a promising approach. The challenge, however, is the relatively complex reaction network. The kinetics of the complete glycerol oxidation network over Pt–Bi/C catalyst was investigated systematically in this study. Based on a detailed reaction mechanism including adsorption/desorption and reaction steps on the catalyst surface, a kinetic model was developed. To overcome the difficulty in finding the global optimum in the model, the full complex network was decomposed into five progressively larger sub-networks with different intermediates as initial reactants. The corresponding reactions starting with these initial reactants were conducted and the collected data were used to fit the kinetic model for each sub-network. The experimental and calculated results were in good agreement and the kinetic parameters for each step were obtained. These results can be used to design and develop new appropriate catalysts with high stability, activity and selectivity for DHA. In fact, this approach is a powerful tool for the microkinetic study of other complex reaction networks as well. Based on the concentration of each component and rate expression of each reaction step, a simplified network was identified and studied. The parameters thus obtained can be used to develop reactor models which could be used to determine the optimum operating reaction conditions for maximizing the yield of desired product DHA. The effective conversion of glycerol to high value chemical will increase the profitability of biodiesel production, a promising renewable energy source.
Keywords: Glycerol oxidation; Mechanism; Kinetics; Parameter estimation; Complex reaction networks
Removal of dibenzothiophenes from model diesel fuel on sulfur rich activated carbons by Mykola Seredych; Teresa J. Bandosz (pp. 133-141).
Display Omitted► Carbons with incorporated sulfur were used as adsorbents of dibenzothiophenes from model diesel fuel. ► The positive effect of sulfur on the capacity/selectivity of adsorption was found. ► Selectivity was enhanced owing to sulfur–sulfur interactions. ► Sulfur in the carbon matrix contributes to activation of oxygen. ► DBT to sulfoxides and sulfones were found as the products of reactive adsorption.Adsorption of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from model diesel fuel with 20ppmw total concentration of sulfur was investigated on commercial wood based carbon exposed to hydrogen sulfide at 650°C and 800°C. The initial and exhausted carbons were characterized using adsorption of nitrogen, thermal analysis, potentiometric titration, FTIR, mass spectroscopy, and elemental analysis. The selectivities for DBT and DMDBT adsorption were calculated with reference to naphthalene. The results showed a marked positive effect of sulfur incorporated to the carbon matrix on the capacity and selectivity for DBT and DMDBT removal from model diesel fuel. This was linked to possible sulfur–sulfur interactions in the whole range of pores. Sulfur in the carbon matrix also contributes to activation of oxygen and oxidation of DBT to sulfoxides and sulfones. Owing to this, not only micropores but also larger pores are active in the selective adsorption.
Keywords: Dibenzothiophenes; Model diesel fuel; Activated carbon; S-Functionalities; Reactive adsorption
Effect of Fe content on physical properties of BaO–CeO x–FeO y catalysts for direct NO decomposition by Won-Jong Hong; Mao Ueda; Shinji Iwamoto; Saburo Hosokawa; Kenji Wada; Hiroyoshi Kanai; Hiroshi Deguchi; Masashi Inoue (pp. 142-148).
Display Omitted► CeO2–Fe2O3 solid solutions with the CeO2 cubic fluorite structure are formed. ► Local structure of iron had a tetrahedral coordination environment. ► Incorporation of Fe3+ in fluorite structure causes the formation of oxygen vacancies. ► Oxygen vacancies play important roles in the NO decomposition activity.The physical properties of the Ba-loaded Ce–Fe mixed oxide catalysts, which exhibited high activity for NO decomposition to N2, were investigated. The optimum Fe/(Ce+Fe) molar ratio was 0.02. The X-ray absorption near edge structure, electron spin resonance, and diffuse reflectance UV–vis spectra indicated that the optimum catalyst had the highest proportion of isolated tetrahedral Fe3+ ions in all the Fe species. Raman spectra suggested that incorporation of Fe3+ in the fluorite structure of CeO2 caused an increase in the concentration of oxygen vacancies, which play an important role in the NO decomposition activity of the catalysts. Temperature-programmed desorption (TPD) of O2 showed that the addition of the Fe component to BaO/CeO2 enhanced O2 uptakes and facilitated oxygen desorption. NO-TPD profiles showed that NO desorption was associated with the desorption of O2, indicating that these two species are formed by decomposition of surface nitrate species.
Keywords: Ce–Fe mixed oxide; Oxygen vacancy; O; 2; -TPD; NO-TPD; NO decomposition
Optimization of the combustion synthesis towards efficient LaMnO3+ y catalysts in methane oxidation by Hend Najjar; Jean-François Lamonier; Olivier Mentré; Jean-Marc Giraudon; Habib Batis (pp. 149-159).
.Display Omitted► LaMnO3 synthesized by combustion method with different glycine/nitrate ratios. ► Their catalytic activity in CH4 oxidation directly related to the specific area. ► Higher catalytic performances for glycine-rich precursors. ► Among the pertinent parameters (Mn4+ concentration, oxygen mobility, crystallite size and SSA), which can account for the proposed mechanisms, the SSA appears to be the most relevant.The present work deals with the synthesis and the study of physico-chemical and catalytic properties of a series of lanthanum manganite perovskite-type oxide using the one-step combustion method. Glycine was used as complexing agent and fuel. Seven glycine-to-nitrate ratios from 0.32 to 0.8 were investigated. XRD patterns show a single phase perovskite type oxide when glycine-to-nitrate ratio is above 0.37. Glycine/nitrate ratio affects significantly the surface areas, which range in 18–37m2/g. The use of fuel-rich precursor allows an enhancement of the specific surface area, the reducibility of manganese and the mobility of desorbed oxygen. The light-off temperature for 50% and 90% of methane conversion was found to be directly related to surface areas. The highest catalytic activity was obtained for glycine-to-nitrate ratio of 0.8, which exhibits the highest superficial concentration of manganese and the highest amount of active oxygen. This catalyst shows also a good thermal stability.
Keywords: Combustion synthesis; Perovskite; Methane oxidation; Active species; Thermal stability
Plasma assisted heterogeneous catalytic oxidation of carbon monoxide and unburned hydrocarbons: Laboratory-scale investigations by Michael J. Kirkpatrick; Emmanuel Odic; Jean-Philippe Leininger; Gilbert Blanchard; Severine Rousseau; Xavier Glipa (pp. 160-166).
.Display Omitted► Heterogeneous oxidation of carbon monoxide by ozone on a diesel oxidation catalyst was observed. ► Non-thermal plasma upstream of catalyst acts mostly to reduce emission of hydrocarbons and not CO. ► Ozone injection upstream of catalyst results in reduction of both CO and hydrocarbon emissions. ► The reduction in CO emission exhibited a rebound effect with ozone injection. ► Energy cost for a 25% reduction in HCs was 77J/L for ozone injection and 120J/L for direct plasma.The use of upstream plasma treatment and ozone injection for the amelioration of the performance of diesel oxidation catalysis was investigated. Experiments presented here were performed in preparation for full scale tests on diesel engines. A significant augmentation of the oxidation rate of carbon monoxide was observed when plasma was applied upstream of a diesel oxidation catalyst and was attributed to a heterogeneous reaction of ozone with carbon monoxide. This observation led to ozone injection being investigated as an alternative to the direct application of dielectric barrier discharge type plasma to the gas upstream of the diesel oxidation catalyst. Results are presented about the two modes of the combination of the non-thermal plasma with the catalyst when they were applied during the catalyst light off, and are compared in terms of pollutant removal and energy cost for carbon monoxide and hydrocarbons. Mechanisms for these effects are proposed and the performances of the two approaches are discussed.
Keywords: Non-thermal plasma; Diesel oxidation catalysis; Ozone; Carbon monoxide; Unburned hydrocarbons
Co-feeding water to attenuate deactivation of the catalyst metallic function (CuO–ZnO–Al2O3) by coke in the direct synthesis of dimethyl ether by Irene Sierra; Javier Ereña; Andrés T. Aguayo; José M. Arandes; Martin Olazar; Javier Bilbao (pp. 167-173).
.Display Omitted► A CuO–ZnO–Al2O3/γ-Al2O3 bifunctional catalyst is used in the direct synthesis of DME. ► The catalyst deactivation is attenuated by co-feeding water with syngas. ► This attenuation is attributed to the inhibition in the formation of methoxy ions. ► Co-feeding water also attenuates the formation of paraffins. ► A water/syngas molar ratio of 0.20 in the feed is suitable to attenuate deactivation with high DME yield.Co-feeding water with syngas in the direct synthesis of dimethyl ether has been studied in order to reduce the deactivation by coke deposition on the CuO–ZnO–Al2O3 metallic function in the CuO–ZnO–Al2O3/γ-Al2O3 bifunctional catalyst. The runs (synthesis of methanol and synthesis of DME) have been carried out in an isothermal fixed bed reactor under conditions avoiding catalyst deactivation due to the sintering of the metallic function (<325°C) and the deactivation of the acid function (with an excess of γ-Al2O3 in the catalyst). The results of long-term experiments evidence that water in the reaction medium attenuates coke deposition during the methanol synthesis step, which is the limiting one. Water is understood to partially inhibit the formation of coke precursor methoxy ions. Furthermore, the formation of paraffins is attenuated by co-feeding water.
Keywords: Dimethyl ether; Methanol; Syngas; STD process; Catalyst deactivation; Coke
Testing PtRu/CNF catalysts for a high temperature polybenzimidazole-based direct ethanol fuel cell. Effect of metal content by Justo Lobato; Pablo Cañizares; Diego Ubeda; Francisco J. Pinar; Manuel A. Rodrigo (pp. 174-180).
.Display Omitted► PtRu/CNF in a DEFC operating at high temperature is reported for the first time. ► The PtRu/CNF showed a very high resistance to the agglomeration in acid media. ► 35mWcm−2 was reached at 200°C, ambient pressure, and 1mgPtcm−2 in both electrodes. ► Catalyst with the higher metal content achieved the higher Ru alloy level.Catalysts with high and low metal contents, Pt–Ru (1:1 molar ratio), supported on carbon nanofibres for the electro-oxidation of ethanol have been studied in a H3PO4-doped polybenzimidazole-based fuel cell, using ethanol fed as a vapour and operating in the temperature range 150–200°C. The catalysts were synthesised using ethylene glycol as a reducing agent and were characterized by X-ray diffraction, TEM, SEM, BET area measurements and temperature-programmed reduction. The catalyst with the highest metal percentage showed the highest Ru alloy level. A similar crystallite size was obtained for both catalysts and oxide species were not detected. Both catalysts showed very high stability to the sintering processes during cyclic voltammetry studies. Moreover, both catalysts were tested in a direct ethanol fuel cell (DEFC) operating at high temperature (125–200°C) and with low Pt loading in both electrodes (1mgPtcm−2). A positive effect of temperature was observed in both cases. The catalyst with 60% PtRu gave the highest activity in ethanol oxidation and the performance was good, which makes PtRu/CNF a promising candidate for use in a DEFC operating at high temperature.
Keywords: Carbon nanofibres; Ethanol; High temperature; Polybenzimidazole membrane; Pt:Ru/CNF
Sterilization of microorganisms on jet spray formed titanium dioxide surfaces by J.W. MacFarlane; H.F. Jenkinson; T.B. Scott (pp. 181-185).
Display Omitted► Jet sprayed nano TiO2 surfaces under UV illumination show rapid destruction of microorganisms. ► Sterilization shows pseudo first order kinetics, faster than previously studies. ► Rate is relatively independent of microbial cell density within the limits examined. ► ROS mechanism proposed as inactivation rates correlated with accessibility of plasma membrane.The photocatalytic inactivation of microorganisms seeded on jet spray formed TiO2 surfaces was studied using ultra-violet LED illumination centered at a wavelength of 388nm. The surfaces were found to be highly effective at eradicating Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans cells, showing no obvious dependence on cell density. Efficiencies of killing were found to show a large variation between species with, in order of susceptibility, P. aeruginosa (gram-negative bacterium)> S. aureus (gram-positive bacterium)> C. albicans (yeast). A mechanism for inactivation based upon oxidation and reduction of cell membranes/walls by photo-generated OH radicals is supported. Those species with relatively thicker and complex cell wall structures ( C. albicans and S. aureus) were destroyed more slowly than P. aeruginosa, which has a thinner cell wall. Electron microscopy examination showed complete mineralization of P. aeruginosa cells upon the TiO2 surface within 25min of illumination. The results presented illustrate the benefit that jet spray formed coatings could have upon the health service with examples including implants and sterile surfaces.
Keywords: Jet-sprayed; TiO; 2; Antibacterial; Surface; Photocatalysis
Coordination state of Cu+ ions in Cu-[Al]MCM-41 by K. Chakarova; G. Petrova; M. Dimitrov; L. Dimitrov; G. Vayssilov; T. Tsoncheva; K. Hadjiivanov (pp. 186-194).
Display Omitted► Deposition of Cu2+ ions on [Al]MCM-41 proceeds without participation of OH groups. ► Cu+ ions in Cu-[Al]MCM-41 have three coordinative vacancies each. ► FTIR spectra of coadsorbed12C16O and13C18O prove polycarbonyl structures.A Cu-[Al]MCM-41 sample was studied by FTIR spectroscopy of probe molecules (CO and NO) and methanol conversion test reaction. It was found that the parent MCM-41 material was characterized by the practical absence of strongly acidic hydroxyl groups (typical of zeolites), but possessed some hydroxyls with a moderate acidity. Introduction of copper to the material by a procedure typical of ion-exchange did not affect the OH groups of MCM-41. However, reduction of the deposited Cu2+ ions resulted in formation of Cu+ ions with a high coordinative unsaturation (typical of Cu+ in zeolites): they were able to adsorb up to three CO molecules each. Adsorption of12C16O–13C18O mixtures was used to prove the polycarbonyl structures. The possible application of Cu-[Al]MCM-41 in environmental catalysis is discussed.
Keywords: Adsorption; CO; Cu-MCM-41; NO; FTIR; Methanol decomposition
Mesoporous material supported manganese oxides (MnOx/MCM-41) catalytic ozonation of nitrobenzene in water by Minghao Sui; Jia Liu; Li Sheng (pp. 195-203).
Display Omitted► MCM-41 supported MnOx as catalyst was introduced into ozonation process. ► MnOx/MCM-41 shows good catalytic activity on ozonation of nitrobenzene in water. ► tert-Butanol has insignificant effect on catalytic ozonation of nitrobenzene ► Stronger DMPO-OH signal intensity was observed in MnOx/MCM-41 catalytic ozonation.Mesoporous material (MCM-41) supported manganese oxides (MnOx) as catalyst was introduced into ozonation process. The catalytic activity of MnOx/MCM-41 on ozonation of nitrobenzene (NB) was evaluated. Both of the indirect method, using tert-butanol (TBA) as a scavenger, and the direct electron spin resonance (ESR) determination technology were employed to investigate whether the high reactivity of MnOx/MCM-41 on ozonation is ascribed to the promotion of the generation of hydroxyl radicals. Though the presence of TBA has insignificant effect on MnOx/MCM-41 catalytic ozonation of NB, stronger signal intensity of DMPO-OH adduct was observed in MnOx/MCM-41 catalytic ozonation than that of in ozonation alone system. Furthermore, the catalytic performance of MnOx/MCM-41 on ozone in different water background (tap water, prepared inorganic and organic water) was investigated.
Keywords: Manganese oxides (MnOx); Mesoporous material (MCM-41); Heterogeneous catalytic ozonation; Nitrobenzene; Hydroxyl radicals
Catalytic conversion of anisole over HY and HZSM-5 zeolites in the presence of different hydrocarbon mixtures by Teerawit Prasomsri; Anh T. To; Steven Crossley; Walter E. Alvarez; Daniel E. Resasco (pp. 204-211).
Display Omitted► Conversion of anisole on acid zeolite produces a range of phenolic compounds via transalkylation. ► Extensive coke formation and strong adsorption of anisole and its products cause rapid deactivation. ► Deactivation is greatly reduced by adding tetralin or other molecules with high H-transfer capacity. ► Other hydrocarbons with weaker H-transfer capacity do little or nothing to prevent deactivation.The conversion of pure anisole (with a methoxy functionality, typical of some bio-oil components) and its mixtures with propylene, n-decane, benzene, or tetralin, has been investigated over zeolites in continuous flow and pulse reactors. The dominant reaction of pure anisole is transalkylation, which produces phenol, cresols, xylenols, and methyl anisoles as main products. However, in the presence of an effective hydrogen donor like tetralin important differences in product distribution are observed. In addition, while with pure anisole in the feed a fast deactivation is observed, the addition of tetralin to the feed results in lower amounts of carbon deposits and much higher catalyst stability. By contrast, less dramatic effects on stability and carbon formation were observed with most of the other co-fed hydrocarbons investigated.
Keywords: Bio-oil; Biomass; Anisole; Phenolics; Hydrogen transfer; Deactivation; HY; HZSM-5; Zeolite
Gram-scale wet chemical synthesis of wurtzite-8H nanoporous ZnS spheres with high photocatalytic activity by Yong Liu; Juncheng Hu; Chilan Ngo; Sergey Prikhodko; Suneel Kodambaka; Jinlin Li; Ryan Richards (pp. 212-219).
Wurtzite-8H nanoporous ZnS spheres assembled from crystallites were synthesized for the first time via a “green” wet chemical route. The catalyst showed high and stable photocatalytic activity for the degradation of persistent organic pollutants as demonstrated with azo dye X-3B (X-3B), trichloroacetate (TCA) and phenol under both visible (>420nm) and UV light irradiation.Display Omitted► “Green” wet chemical route for the gram-scale synthesis of ZnS spheres. ► Composition is hexagonal wurtzite ZnS nanosheets (∼600nm in diameter). ► Photocatalytic decomposition of azo dye, trichloroacetate, and phenol. ► Photocatalysis under both visible and UV irradiation.Wurtzite-8H nanoporous ZnS spheres assembled from crystallites, were synthesized via a “green” wet chemical route. A possible formation mechanism for the growth process of the ZnS spheres has been proposed based on experimental observations. The prepared catalysts are characterized by transmission electron microscopy, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, N2 adsorption–desorption isotherms, elemental analysis, and UV–vis absorption spectroscopy. The catalyst showed high and stable photocatalytic activity for the degradation of persistent toxic organic pollutants, as demonstrated with azo dye X-3B (X-3B), trichloroacetate (TCA) and phenol under both visible (>420nm) and UV light irradiation. The experimental results demonstrate that the photocatalytic activity of ZnS spheres is 3.3 and 9 times higher than that of Degussa P25 and commercial ZnS, respectively. The production ofOH radicals on the ZnS surface was detected by the photoluminescence (PL) technique using coumarin as a probe molecule, which suggests thatOH radicals are the dominant photo-oxidant in the photocatalytic reaction. More importantly, this synthesis method can be economical for a scale-up process, and may also be applicable to the preparation of additional II–VI semiconductors for catalysis and other applications.
Keywords: Nanoporous ZnS spheres; Wurtzite; Photocatalysis; Organic pollutants; Hydroxyl radical (; OH); Photoluminescence technique
Improvement in the methylene blue adsorption capacity and photocatalytic activity of H2-reduced rutile-TiO2 caused by Ni(II)porphyrin preadsorption by Carlos A. Páez; Stéphanie D. Lambert; Dirk Poelman; Jean-Paul Pirard; Benoît Heinrichs (pp. 220-227).
Display Omitted► A high surface coverage of NiTCPP in TiO2-xerogel (Ti-NC) was achieved by calcination at 700°C and high temperature reduction at 400°C under hydrogen flow. ► Calcination/reduction treatment also caused an increase in the number of TiO2-surface active sites for the NiTCPP-adsorption. ► The presence of NiTCPP-molecules in the H2-reduced rutile-TiO2 xerogel surface led to a significant enhancement in its MB-adsorption capacity. This result was probably achieved due to the generation of new rutile-TiO2 surface active sites for MB-adsorption with high electronic density, such as carboxy-porphyrin substituent groups. ► The presence of NiTCPP-molecules in the H2-reduced rutile-TiO2 xerogel surface led to a significant enhancement in its MB-photocatalytic capacity, under visible light irradiation. This result could be due to a combined effect of the potential photosensitivity of the rutile-TiO2 band gap, the increase in MB-adsorption capacity and the electron transfer from photo-excited porphyrin to the surface of Ti-700.H2-reduced rutile-TiO2 xerogel (Ti-700), obtained via the sol–gel process, was found to strongly adsorb the Ni(II)-5,10,15,20-tetrakis(4-carboxyphenyl)-porphyrin (NiTCPP) from a methanolic solution, despite its very low specific surface area ( SBET≈2m2g−1). UV/vis spectroscopy analysis showed that after calcination at 700°C and reduction under H2 flow at 400°C, the TiO2-xerogel increased its NiTCPP-adsorption capacity by surface area unit by up to 120 times. The effect of the porphyrin presence in the catalytic performances of TiO2-xerogels was studied through three kinetics models: (i) the pseudo-first-order kinetic model; (ii) the pseudo-second-order kinetic model, which are used to describe the adsorption rate based on the adsorption capacity of the catalysts; and (iii) the Langmuir–Hinshelwood kinetic model which is used to describe the photocatalytic degradation rate of methylene blue (MB). A significant improvement in the efficiency of Ti-700 was observed after the porphyrin-adsorption process (NiTCPP/Ti-700): MB-adsorption capacity at equilibrium and the apparent MB-photoconversion constant, kapp, of NiTCPP/Ti-700 were both up to 2 times higher than those observed for the Ti-700.
Keywords: Reduced TiO; 2; Rutile; Ni(II)-porphyrin; Methylene blue photodegradation; Visible irradiation; Sol–gel process
Synergistic structural and surface promotion of monometallic (Pt) TWCs: Effectiveness and thermal aging tolerance by A. Papavasiliou; A. Tsetsekou; V. Matsouka; M. Konsolakis; I.V. Yentekakis; N. Boukos (pp. 228-241).
Highly effective and thermally stable monometallic (Pt) three way converters were developed by means of synergistic structural (by Ce0.8La0.2O1.9) and surface (by Na) promotion. Their remarkable aging tolerance can be rationalized by the in situ formation of β/β″-alumina phases which preserves alkali–noble metal interactions.Display Omitted► Synergy between structural and surface-induced promotion in TWCs is demonstrated. ► The synergy provides very effective and thermally stable doubly-promoted catalysts. ► The remarkable aging tolerance is related with the in situ formation of β″-alumina. ► The preserved promotion after aging overcomes losses due to textural degradation.Highly effective and thermally stable monometallic (Pt) three way converters (TWCs) with very low Pt loading (0.5wt%) were developed through synergistic structural and surface promotion by modifying the TWC washcoat with 20wt% of Ce0.8La0.2O1.9 (structural promoter) and sodium in the range 5–15wt% (surface promoter). The catalytic performance of the as prepared doubly-promoted Pt(Na)/Al2O3-(Ce0.8La0.2O1.9) catalytic systems, in both “fresh” and “aged” (at 900°C) states, was studied and compared with that of a commercial bimetallic (Pt/Rh) TWC. The catalytic measurements were performed on coated cordierite monoliths, the whole concept simulating real automotive exhaust conditions at the stoichiometric point. An extensive characterization study, involving thermo-gravimetric analysis (TGA/DTA), scanning and transmission electron microscopy (SEM, TEM), X-ray diffraction (XRD), N2 porosimetry and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), was undertaken in order to gain insight and correlate the structural/textural characteristics of these novel catalytic systems with their performance and substantial thermal aging tolerance. Optimum behavior in terms of both catalytic efficacy in simulated TWC conditions and thermal durability, even in comparison with the commercial bimetallic TWC with ∼4.5-fold higher precious metal loading, was demonstrated by the doubly promoted Pt(Na)/Al2O3-(Ce0.8La0.2O1.9) sample with the higher sodium loading of 15wt% Na. The formation of β″-alumina during aging treatment, providing intimate alkali–noble metal contact and therefore preserving their electronic interactions, suggests the mechanism for the enhanced thermal durability and the origin of the remained after aging alkali action.
Keywords: Structural promotion; Electropositive promotion; β/β″-Al; 2; O; 3; Simulated exhaust conditions; Thermal aging
Roles of different intermediate active species in the mineralization reactions of phenolic pollutants under a UV-A/C photo-Fenton process by J.M. Monteagudo; A. Durán; I. San Martin; A. Carnicer (pp. 242-249).
Display Omitted► We have studied the mineralization of phenolic mixture under a UV-A/C photo-Fenton system. ► In the absence of scavenging agents, 88% TOC removal of the phenolic mixture was achieved in 60min. ► Superoxide radical anions and triplet oxygen were the main oxidants in earlier stages. ► Singlet oxygen, hydroxyl and hydroperoxy radicals played more significant roles in later stages. ► Tert-butyl alcohol was the most significant scavenger that affected the inhibition of reaction.The roles of different intermediate oxidative species, such as singlet oxygen, triplet oxygen, superoxide radical anions and hydroperoxy or hydroxyl radicals, were studied in the mineralization reactions of solutions containing a mixture of three phenolic compounds (namely gallic, p-coumaric and protocatechuic acids). The degradation process that was developed was a ferrioxalate-induced artificial ultraviolet (UV)-A/C photo-Fenton system. Reactions were carried out in an UV reactor consisting of two 50-W UV-C lamps and two 75-W UV-A lamps. The roles played by the oxidative active species in various stages of the process were determined by running the reaction in the presence of different scavenging agents. Analyses were conducted within a multivariate experimental design combined with neural networks that included the following variables: initial concentrations of tert-butyl alcohol, 1,4-benzoquinone, sodium azide and potassium iodide. The response function was the %TOC removal after 15 and 60min of reaction. Under optimal conditions (e.g., in the absence of scavenging agents), 88% TOC removal of the phenolic mixture could be achieved in 60min at 28°C. Superoxide radical anions and triplet oxygen were the main oxidants in earlier stages of the mineralization of this phenolic-mixture solution, whereas singlet oxygen, hydroxyl and hydroperoxy radicals played more significant roles in later stages. Tert-butyl alcohol was the most significant scavenger affecting inhibition of the mineralization reaction, as it trapped almost all of the intermediate active species.
Keywords: Radical scavenger; Gallic; Coumaric; Protocatechuic; Ferrioxalate; Photo-Fenton
Photofuel cells using glucose-doped titania by Hiromasa Nishikiori; Kazuhiro Isomura; Yohei Uesugi; Tsuneo Fujii (pp. 250-254).
Display Omitted► Glucose-doped titania electrodes were prepared by a sol–gel method. ► Photocatalytic oxidation of the glucose enhanced the generation of electricity. ► Steam treatment of the electrodes improved the glucose oxidation and the electricity. ► CO2 and H2O were observed as the photocatalytic products. ► The contact between the glucose and titania is important for the high reactivity.Glucose-doped titania electrodes were prepared from titanium alkoxide sols containing glucose in order to examine the validity of the fuel material concentrated on the photocatalyst surface. The observed photocurrent and CO2 and H2O productions indicated that the oxidation of the glucose enhanced the generation of electricity during the UV irradiation. Steam treatment of the electrodes improved the glucose oxidation and the photocurrent. However, refluxing of the precursor sol did not improve them. Not only the titania conductivity, but also the contact between the glucose and titania is important in order to obtain a high photofuel electric conversion. The concentration of the fuel material on the photocatalyst surface improved the energy conversion efficiency.
Keywords: Photofuel cell; Titania; Photocatalysis; Glucose; Oxidation
Sulfur-tolerant lanthanide oxysulfide catalysts for the high-temperature water–gas shift reaction by Ioannis Valsamakis; Maria Flytzani-Stephanopoulos (pp. 255-263).
Display Omitted► Lanthanide oxysulfides active catalysts for high temperature WGS and RWGS reactions. ► Reaction lights off ∼400°C and above 750°C equilibrium conversions are reached. ► No loss of sulfur with time-on-stream over the temperature range from 400 to 800°C. ► Superior performance than commercial Fe–Cr in gas feed containing 700ppm H2S. ► Complete sulfur tolerance at 800°C and partial inhibition at 600°C with 700ppm H2S.We report on the high activity and stability of lanthanide oxysulfides, e.g., of La2O2S or Pr2O2S, as catalysts for the high temperature water–gas shift (WGS) and the reverse water gas shift (RWGS) reactions. The catalytic activity derives from a very large oxygen storage capacity based on the redox of the sulfur ion in the interconverting oxysulfide/oxysulfate phases during reaction. The WGS reaction lights off at around 400°C and reaches equilibrium at temperatures >750°C in tests conducted at high space velocities (∼14,000h−1). No loss of sulfur or catalyst deactivation is observed with time-on-stream in sulfur-free gas mixtures at all temperatures. These catalysts have fivefold lower aerial reaction rates (μmol/m2/s) than commercial Fe–Cr catalysts at 400°C. However, unlike the iron oxide-based catalysts, they can be used up to 800°C with high levels of H2S (700ppm) present in the gas mixture. Inhibition by sulfur at lower temperatures was fully reversible.
Keywords: Water–gas shift reaction; Sulfur tolerant catalysts; Reverse water–gas shift; Rare earth oxysulfides; Fuel cells; Hydrogen generation
Catalytic activity of Fe/SBA-15 for ozonation of dimethyl phthalate in aqueous solution by Ruihuan Huang; Huihua Yan; Laisheng Li; Dayi Deng; Yuehong Shu; Qiuyun Zhang (pp. 264-271).
Display Omitted► The mesoporous Fe/SBA-15 was used as a heterogeneous catalyst for ozonation of dimethyl phthalate (DMP) in aqueous solution. ► The mineralization rate constant of DMP with Fe/SBA-15/O3 is 3.9 times with that of O3 alone. ► There is a synergetic effect between O3 and Fe/SBA-15 adsorption. ► Fe/SBA-15 is a promising heterogeneous catalyst for ozonation of organic pollutants in aqueous solution.The catalytic activity of iron-loaded SBA-15 (Fe/SBA-15) for ozonation of dimethyl phthalate (DMP) in aqueous solution was investigated. SBA-15 was synthesized by a hydrothermal method and Fe/SBA-15 was prepared by an incipient wetness impregnation method. The materials were characterized by a low and wide angle X-ray powder diffraction (XRD), N2 adsorption–desorption, and atomic absorption spectrometer (AAS). Under the chosen conditions (50mgh−1 ozone dosage, 10mgl−1 DMP solution and 0.20gl−1 catalyst dosage), Fe/SBA-15/O3 process obviously improved DMP and total organic carbon (TOC) removal efficiency due to the generation of hydroxyl radical (HO), which was approved by tert-butanol (TBA). The mineralization of DMP followed an apparent first-order kinetics. The rate constant in Fe/SBA-15/O3 was 0.0058min−1, 3.9 times higher than that of O3 alone, 3.4 and 1.9 times higher than those of SBA-15/O3 and Fe2O3/O3 processes respectively. The iron content, reaction temperature and initial pH of DMP solution played important roles in Fe/SBA-15/O3 process, while chloride ion exhibited the slight influence. The synergetic effect between O3 and Fe/SBA-15 adsorption illustrates that Fe/SBA-15 is a promising catalyst for ozonation process.
Keywords: Fe/SBA-15; Catalytic ozonation; Dimethyl phthalate