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Applied Catalysis B, Environmental (v.79, #1)
Synthesis and characterization of high performance Pt-(Pr xCe yO z)/C catalysts for methanol electrooxidation by Zhicheng Tang; Gongxuan Lu (pp. 1-7).
In this paper, Pr xCe yO z ( x/ y=3/1, 1/1, 1/3) modified Pt/C catalysts were prepared by wet precipitation and reduction method. The catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). TEM showed that Pt nanoparticles were uniformly dispersed on the surface of carbon support with an average particle size of 4.0–5.0nm in the Pt-(Pr xCe yO z)/C catalysts. XRD showed that all the Pt-(Pr xCe yO z)/C catalysts displayed the typical character of Pt face centered cubic (fcc) phase. XRD and EDX analysis indicated that the rare earth oxides exist in an amorphous form. The Pt-(Pr xCe yO z)/C electrocatalysts were compared with the Pt/C, Pt3-(PrO x)1/C and Pt3-(CeO x)1/C catalysts in terms of electrochemical activity and stability for methanol electrooxidation using cyclic voltammetry (CV) and chronoamperometry (CA) in 0.5M H2SO4+0.5M CH3OH solutions. The CO-tolerance experiment was measured in the CO-saturated 0.5M H2SO4 solutions. The results showed that the Pt-(Pr1Ce1O z)/C catalyst had the highest catalytic activity, the best stability and CO-tolerance, which could be used as a suitable electrocatalyst for direct methanol fuel cell.
Keywords: Methanol electrooxidation; Direct methanol fuel cell; Rare earth oxides; Electrocatalyst; Electrocatalytic reaction
Photoactivities of the visible-light-activated mixed-phase carbon-containing titanium dioxide: The effect of carbon incorporation by Sergey Y. Treschev; Po-Wen Chou; Yao-Hsuan Tseng; Jia-Bin Wang; Elena V. Perevedentseva; Chia-Liang Cheng (pp. 8-16).
Photoactivities of the carbon-containing nano-structured titanium dioxide (TiO2) prepared using a modified sol–gel method as visible-light-responsive photocatalysts were studied. This research aimed to compare four carbon-containing TiO2 samples, prepared in different conditions, with a commercial nano-structured TiO2 powders. The prepared titanium dioxide powders were analyzed using Raman spectroscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy. It is found carbon-containing TiO2 nanoparticles prepared under calcinations at 200°C exhibited high photocatalytic activity for decoloring of methylene blue and the removal of nitrogen monoxide under both ultraviolet and visible-light illumination. The calcination temperature and incorporated carbons affect the particle size and lattice structure of TiO2, and hence the photoactivities. The superior photocatalytic effects were attributed to the carbon-containing mixed anatase and rutile phase in the crystal structure of the TiO2.
Keywords: Visible-light-activated TiO; 2; Carbon-containing TiO; 2; Confocal Raman mapping; Photoactivity
Ethanol steam reforming over Rh/Ce xZr1− xO2 catalysts: Impact of the CO–CO2–CH4 interconversion reactions on the H2 production by Anne Birot; Florence Epron; Claude Descorme; Daniel Duprez (pp. 17-25).
Ce xZr1− xO2 mixed oxide-supported 1wt.%Rh catalysts were prepared by wet impregnation using Rh nitrate as a precursor and calcined at 900°C. They were characterized by BET surface area, XRD, CO2 chemisorption and H2 chemisorption at −85°C and tested in the ethanol steam reforming at 600°C under atmospheric pressure, with water to ethanol molar ratio equal to 4, without carrier gas. The best performances, i.e. the highest hydrogen yield and the lowest coke deposition, were obtained over Rh/Ce0.5Zr0.5O2, i.e. 3.63mol H2/molethanol. This catalyst was subsequently evaluated under various reaction conditions. Whatever the temperature and the water to ethanol ratio, the ethanol steam reforming yielded a large amount of methane, which tends to reduce the H2 production. To elucidate the origin of the methane production, CO/CO2/CH4 interconversion reactions were studied. It was shown that such catalyst favours the formation of methane via CO hydrogenation. The direct hydrogenation of CO2 was not observed. In parallel, the catalyst was active in the reverse water gas shift (RWGS) reaction between CO2 and H2, leading CO and H2O.
Keywords: Ethanol steam reforming; Rh/ceria–zirconia catalysts; CO and CO; 2; hydrogenation; Water gas shift; Reverse water gas shift
Mesoporous CuO–Fe2O3 composite catalysts for low-temperature carbon monoxide oxidation by Jian-Liang Cao; Yan Wang; Xiu-Ling Yu; Shu-Rong Wang; Shi-Hua Wu; Zhong-Yong Yuan (pp. 26-34).
A series of mesoporous CuO–Fe2O3 composite oxide catalysts with different CuO contents were prepared by a surfactant-assisted method of nanoparticle assembly. The prepared composite oxides were characterized by X-ray diffraction, N2 adsorption, transmission electron microscopy, hydrogen temperature-programmed reduction, thermogravimetry–differential thermal analysis and X-ray photoelectron spectroscopy. Their catalytic behavior for low-temperature CO oxidation was studied by using a microreactor-GC system. These mesoporous CuO–Fe2O3 catalysts possess a wormhole-like mesostructure with a narrow pore size distribution and high surface area, exhibiting high catalytic activity and stability for low-temperature CO oxidation. The catalytic behavior depended on the CuO content, the precalcination temperature, the surface area and the particle size of the catalysts. The catalyst with 15mol% CuO content and calcined at 300°C exhibited the highest catalytic activity and stability.
Keywords: CuO–Fe; 2; O; 3; catalyst; Mesoporous; CO oxidation; Catalytic activity
Solvent free selective oxidation of benzyl alcohol to benzaldehyde using a membrane contactor unit by M.G. Buonomenna; E. Drioli (pp. 35-42).
A new clean catalytic process for the selective oxidation of benzyl alcohol with hydrogen peroxide to benzaldehyde has been studied. Neither solvent nor promoters are needed: a polymeric microporous membrane acts as a barrier to “keep in contact” the two phases: the organic phase, containing the substrate and the product, and the aqueous phase with the oxidant. Being the two phases separated by the membrane, there is no mix of them and dispersion phenomena do not occur. The species are transferred from one phase to the other only by diffusion.The effect of various reaction parameters such as reaction temperature, type of membrane, type of catalyst, the addition mode of hydrogen peroxide was investigated.Three different membranes based on hydrophobic polyvinilidene fluoride (PVDF) were prepared by phase inversion technique induced by nonsolvent and used as membrane contactor. The membranes are characterized by different thicknesses, porosity, tortuosity and hydrophobicity. The catalysts used were ammonium molybdate, (NH4)6Mo7O24 and sodium tungstate, Na2WO4. In literature, both these catalysts were reported to be effective in the oxidation of alcohols with H2O2 in combination with a phase transfer catalyst in chlorinated solvents.
Keywords: Selective oxidation; Solvent free reaction; Hydrogen peroxide; Membrane contactor; Sustainable process
Catalytic dechlorination of gas-phase perchloroethylene under mixed redox conditions by Özer Orbay; Song Gao; Brian Barbaris; Erik Rupp; A. Eduardo Sáez; Robert G. Arnold; Eric A. Betterton (pp. 43-52).
The validity of a new method to destroy gas-phase perchloroethylene (PCE) is demonstrated at bench scale using a fixed-bed reactor that contains a Pt/Rh catalyst. Hydrogen and oxygen were simultaneously fed to the reactor together with PCE. The conversion efficiencies of PCE were sensitive to H2/O2 ratio and reactor temperature. When the temperature was ≥400°C and H2/O2 was ≥2.15, PCE conversion efficiency was maintained at ≥90%. No catalyst deactivation was observed for over 2 years, using only mild, convenient regeneration procedures. It is likely that PCE reduction steps precede oxidation reactions and that the importance of oxidation lies in its elimination of intermediates that would otherwise lead to catalyst poisoning. In practice, this catalytic dechlorination method holds potential for low-cost, large-scale field operation.
Keywords: PCE destruction; Catalytic dechlorination; Redox conditions; Reduction; Oxidation
Flame-made WO3/TiO2 nanoparticles: Relation between surface acidity, structure and photocatalytic activity by Kranthi K. Akurati; Andri Vital; Jean-Philippe Dellemann; Katarzyna Michalow; Thomas Graule; Davide Ferri; Alfons Baiker (pp. 53-62).
WO3/TiO2 composite nanoparticles have been synthesized by dissolving W and Ti precursors in a suitable solvent and spraying into a high temperature acetylene-oxygen flame using a reactive atomizing gas. Particles with controlled W:Ti ratios were produced at various flow rates of precursor solution and the resulting powders were characterized by Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman and attenuated total reflection infrared (ATR-IR) spectroscopy. Two-dimensional coordinatively unsaturated wolframyl species were well dispersed on the TiO2 surface for the samples with equal to or less than 3.6mol% WO3 and contributed to an increase of the surface acidity. Crystalline WO3 was formed for samples with >3.6mol% WO3. Formation of crystalline WO3 is attributed to the enhanced rate of condensation of W species with increasing loading of tungsten. Variation of λ (defined as the ratio of the actual oxygen-to-fuel ratio of the reactants to the stoichiometric oxygen-to-fuel ratio) influences the residence time of the particles in the high temperature flame and affects the type of surface species and thereby the resultant acidity. The photocatalytic activity of the composite particles was tested for the degradation of methylene blue (MB) and was compared with that of commercial Degussa P25-TiO2. The improved photocatalytic activity of the composite particles is attributed to the increased surface acidity and better charge separation due to the coupling of WO x species and TiO2 within the composite nanoparticles.
Keywords: Abbreviations; FSS; flame spray synthesis; PCA; photocatalytic activity; TTIP; titanium tetraisopropoxide; AMT; ammonium metatungstate; DMF; dimethyl formamide; CED; combustion enthalpy density; SSA; specific surface area; MCT; mercury–cadmium–telluride; MB; methylene blue; FWHM; full width at half maximum; HyCOM; hydrothermal crystallization in organic mediaLewis acids; Acidity; Raman spectroscopy; Photocatalysis; Nanoparticles; Flame spray synthesis; Adsorption; WO; 3; TiO; 2
Photocatalytic discoloration of Methyl Orange on innovative parylene–TiO2 flexible thin films under simulated sunlight by Yu Zhiyong; H. Keppner; D. Laub; E. Mielczarski; J. Mielczarski; L. Kiwi-Minsker; A. Renken; J. Kiwi (pp. 63-71).
Parylene films loaded with TiO2 are reported as photocatalysts in azo dye discoloration processes. The TiO2 loading of the parylene film was 0.32% (w/w) and the amount of TiO2 on the film was about two orders of magnitude below the TiO2 added in suspension to discolore the same solution of Methyl Orange used as a probe. The parylene/TiO2 films showed a similar activity in the presence of O2 or H2O2 during the discoloration of dyes. This shows the efficient role of O2 as ecb− scavenger. The photonic efficiency of the parylene/TiO2 film during the Methyl Orange discoloration was 0.04. Based on X-ray photoelectron spectroscopy (XPS) data, the TiO2 particles loaded on the parylene film were shown to be at first encapsulated in the polymer. After the encapsulation is broken, the TiO2 particles are fully exposed to the dye solution. The lack of surface intermediates like C-residues, N and S-species after the photocatalytic process implies an efficient decomposition of the dye at the catalyst interface. During the dye degradation carbonates and carboxylates were detected by XPS and Fourier transform infrared spectroscopy (FTIR) disappearing at the end of the discoloration process. Evidence is presented during the photocatalysis for the formation of a composite parylene/TiO2 film. The formation of this composite involves surface modification of parylene (partial lost of chlorine) in the outermost surface layer with concomitant densification of the TiO2 particles on the parylene film. The parylene film presented a side with high rugosity and one with low rugosity attaching different amounts of TiO2 in each case as observed by transmission electron microscopy (TEM).
Keywords: Parylene films; Discoloration of azo dye; Photocatalysis; TEM; IR; XPS
Simple fabrication of twist-like helix N,S-codoped titania photocatalyst with visible-light response by Jian-Hua Xu; Jingxia Li; Wei-Lin Dai; Yong Cao; Hexing Li; Kangnian Fan (pp. 72-80).
Visible-light responsible N,S-codoped titania photocatalyst was fabricated by simple hydrolysis of titania tetrachloride using ammonia in the presence of glacial acetic acid and ammonium sulfate. The N,S-codoped titania materials were fabricated by a template-free route and demonstrated twist-like helix morphology. The morphology and microstructure characteristics of N,S-codoped titania photocatalysts were characterized by means of the N2 adsorption–desorption measurements, thermal gravimetric and differential thermal analysis (TG-DTA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), UV–visible diffuse reflectance spectra (DRS) and X-ray powder diffraction (XRD). The unique morphology of N,S-codoped titania materials and mesoporous microstructure were maintained after a heat treatment at 723K for 3h, exhibiting significantly thermal stability. The photocatalytic activity was evaluated by degrading phenol in aqueous suspension under ultraviolet and visible light irradiation. The results obtained with these novel photocatalysts are compared with the behavior of the well-studied and widely used Degussa P25 TiO2 under the same conditions. The N,S-codoped titania samples were more superior than P25 and the sample calcined under 723K for 3h shows the best photocatalytic activity, the higher activity of which could be attributed to its high surface area, large pore volume, well-crystallized anatase, red-shift in adsorption edge and strong absorbance of light with longer wavelength.
Keywords: Titanium dioxide; Titanium tetrachloride; Mesoporous; Visible-light; N,S-codoped; Photocatalyst
Dinitrogen photofixation properties of different titanium oxides in conducting polymer/titanium oxide hybrid systems by K. Hoshino; R. Kuchii; T. Ogawa (pp. 81-88).
Titanium oxide layers prepared by hard (rutile and anatase types) and soft processes (anodic amorphous oxides prepared in an aqueous phosphoric,TiOxw, and a dichloromethane/electrolyte solution,TiOxo) were brought into contact with the ClO4−-doped poly(3-methylthiophene) (P3MeT) film, and their ability to photofix atmospheric dinitrogen was compared. The comparisons revealed that the latter junctions using amorphous oxides produced larger amount of N2-fixation products than the former two junctions and that the P3MeT/TiOxw junction exhibited a higher N2-fixation rate than the P3MeT/TiOxo cell. TheTiOxw andTiOxo layers were characterized by transmission electron microscopic observations, X-ray electron dispersive analysis, and selected area electron diffraction measurements, and the higher activity of theTiOxw layer was rationalized on the basis of the contact potential difference measurements. Additionally, the dependences of the N2-fixation yield on the photoirradiation time, P3MeT film thickness, and anodizing potential during the formation of theTiOxw were investigated using the most active P3MeT/TiOxw junction cell.
Keywords: Nitrogen fixation; Conducting polymers; Titanium oxide; Anodic titanium oxide; Light-to-chemical energy conversion
Nitrogen-doped carbon nanostructures and their composites as catalytic materials for proton exchange membrane fuel cell by Yuyan Shao; Jiehe Sui; Geping Yin; Yunzhi Gao (pp. 89-99).
The research and development of catalysts with high activity and high durability is a significant issue for proton exchange membrane fuel cell (PEMFC). Nitrogen-doped carbon nanostructures and their composites demonstrate promising potential for PEMFC catalysts application. The nitrogen doping strategies of carbon nanostructures and the electrocatalytic aspects of nitrogen-containing carbon with and without catalytic metals on it are reviewed. Pt-based catalysts with nitrogen-doped carbon as support exhibit enhanced catalytic activity and durability toward oxygen reduction and methanol oxidation, which can be attributed to the high dispersion of Pt nanoparticles and the modified interaction between Pt nanoparticles and the support. For most of the non-Pt metal catalysts (Fe, Co, etc.) presently investigated for potential application in PEMFC, nitrogen is the indispensable element, and even though there are still controversies, the pyridinic type nitrogen is generally considered to be responsible for the catalytic sites. But the catalytic activity is still low and the stability issue is another challenging problem for non-Pt metal catalysts. Nitrogen-doped carbon, without catalytic metals on it, also shows enhanced catalytic activity. But many issues still need further investigation in order to get catalysts with targeted activity and durability.
Keywords: Proton exchange membrane fuel cell; Nitrogen doping; Carbon nanostructures; Non-Pt catalysts; Oxygen reduction; Durability