Nd- or Zr-modified CuO-CeO2/Al2O3/FeCrAl monolithic catalysts for preferential oxidation of carbon monoxide in hydrogen-rich gases

This work presents a study on the role of the additives over CuO-CeO₂/Al₂O₃/FeCrAl monolithic catalysts for the preferential oxidation of CO. The monolithic catalysts were prepared by in situ combustion method and characterized using SEM, XRD and TPR techniques. The results show that the addition of neodymium or zirconium in the CuO-CeO₂/Al₂O₃/FeCrAl catalysts influences the dispersion state of copper oxide and ceria, lowers the activity of hydrogen oxidation and broadens the temperature window for total CO-conversion.     

Chemical and structural properties of ternary post-transition metal oxide thin films: InZnO,InGaO and GaZnO

The chemical states of ternary post-transition metal oxide thin films of InGaO, GaZnO and InZnO were investigated using X-ray photoelectron spectroscopy. Detailed binding energy (BE) analyses revealed certain evolution in chemistry in the ternary oxides compared to the reference binary oxides of In₂O₃, ZnO, or Ga₂O₃. In particular, O 1s BEs were changed with the compositions, which suggests that the charge transfer (CT) between In³⁺/Ga³⁺/Zn²⁺ and O²⁻ ions is significant. Results of extended X-ray absorption fine structure analyses further showed that the first shell coordination (cation–O bond) is roughly maintained even though the ternary oxide films were structurally disordered. This implies that the CT process via O²⁻ ions can influence the charge reconstructions in the ternary oxide systems.     

The use of acids,niobium oxide,and zeolite catalysts for esterification reactions

We have evaluated the influence of alcohol/fatty acid molar ratio (methanol or ethanol), water and catalyst concentrations and temperature by the esterification of palm fatty acids by heterogeneous acid catalysts (varying types, forms, and particle size). Polynaphtalene sulfonic acid (PSA) and niobium oxide (Nb₂O₅) presented better performance than zeolite catalysts. Reaction with methanol presented higher conversion than with ethanol. The experimental design showed that the most relevant variable is the catalyst concentration and all interactions become important in process. A heterogeneous kinetic model was proposed and applied to experimental data. One of the models was adequate for methanol reaction, whereas the homogeneous model was more appropriate for ethanol reaction. Copyright © 2009 John Wiley & Sons, Ltd.     

Sensitivity of styrene oxidation reaction to the catalyst structure of silver nanoparticles

This study shows how different morphologies of silver nanoparticles affect the selective oxidation of styrene in the gas phase using oxygen as oxidant. Silver nanoparticles (nanowires and nanopolyhedra), prepared using the polyol process, were supported on α-Al₂O₃. For comparison, a conventional catalyst obtained by wet impregnation was also prepared. Phenylacetaldehyde (Phe) and styrene oxide (SO) were the main products for nanoparticles catalysts. The promotion effect on the catalytic activity of potassium and cesium on the silver nanowires catalysts was also studied. At 573 K, the styrene conversion and selectivity to styrene oxide with the silver nanowires catalyst were 57.6 and 42.5%, respectively. Silver nanopolyhedra catalyst showed 57.5% conversion and 30.8% selectivity to styrene oxide. The promotion by cesium played an important role in improving the epoxidation of styrene. The samples were structurally characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) were applied to characterize the oxygen species detected (O_β, O_γ) on the silver surface.     

Hydrogenation of p-chloronitrobenzene on Ni–B Nanometal Catalysts

A series of Ni–B catalysts were prepared by mixing nickel acetate in 50% ethanol/water or methanol/water solution. The solution of sodium borohydride (1 M) in excess amount to nickel was then added dropwise into the mixture to ensure full reduction of nickel cations. The mol ratio of boron to nickel in mother solution was 3 to 1. The effects of preparation conditions such as temperature, stirring speed, and sheltering gas on the particle size, surface compositions, electronic states of surface atoms and catalytic activities of the Ni–B catalysts were studied. Ranel nickel catalyst was included for comparison. These catalysts were characterized by N₂ sorption, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalysts were tested for liquid phase hydrogenation of p-chloronitrobenzene. All of the catalysts prepared in this study had nanosized particles. The preparation condition has significant influence on the particle size and surface compositions of the catalyst. The Ni–B catalyst was passivated by boron; therefore it was more stable than Raney nickel and did not catch fire after exposure to air. The catalysts prepared under N₂ flow could suppress the oxidation of Ni by the dissolved oxygen in water and had metallic state of nickel. The catalyst prepared with vigorous stirring at 25°C under N₂ stream yielded the smallest particles and resulted in the highest activity. It was much more active than the Raney nickel catalyst. The reaction condition also has pronounced effect on the hydrogenation activity. Using methanol as the reaction solvent increased p-chloronitrobenzene conversion to a large extent, compared to that using ethanol as the reaction medium. The selectivity of main product (p-chloroaniline) was greater than 99% on all of the Ni–B catalysts.     

Robust Multi-Objective Optimization for Response Surface Models Applied to Direct Low-Value Natural Gas Conversion Processes

The high proportion of CO₂/CH₄ in low aggregated value natural gas compositions can be used strategically and intelligently to produce more hydrocarbons through oxidative methane coupling (OCM). The main goal of this study was to optimize direct low-value natural gas conversion via CO₂-OCM on metal oxide catalysts using robust multi-objective optimization based on an entropic measure to choose the most preferred Pareto optimal point as the problem’s final solution. The responses of CH₄ conversion, C₂ selectivity, and C₂ yield are modeled using the response surface methodology. In this methodology, decision variables, e.g., the CO₂/CH₄ ratio, reactor temperature, wt.% CaO and wt.% MnO in ceria catalyst, are all employed. The Pareto optimal solution was obtained via the following combination of process parameters: CO₂/CH₄ ratio = 2.50, reactor temperature = 1179.5 K, wt.% CaO in ceria catalyst = 17.2%, wt.% MnO in ceria catalyst = 6.0%. By using the optimal weighting strategy w₁ = 0.2602, w₂ = 0.3203, w₃ = 0.4295, the simultaneous optimal values for the objective functions were: CH₄ conversion = 8.806%, C₂ selectivity = 51.468%, C₂ yield = 3.275%. Finally, an entropic measure used as a decision-making criterion was found to be useful in mapping the regions of minimal variation among the Pareto optimal responses and the results obtained, and this demonstrates that the optimization weights exert influence on the forecast variation of the obtained response.     

Effect of combination of noble metals and metal oxide supports on catalytic reduction of NO by H2

We investigated the effects of combination of noble metals M (Rh, Pd, Ir, Pt) and metal oxide supports S (Al₂O₃, SiO₂, ZrO₂, CeO₂) on the NO + H₂ reaction using planar catalysts with M/S two layered thin films on Si substrate. In this study, NO reduction ability per metal atom were evaluated with a specially designed apparatus employing pulse valves for the injection of reactant molecules onto catalysts and a time-of-flight mass spectrometer to measure multiple transient products: NH₃, N₂ and N₂O simultaneously as well as with an atomic force microscopy to observe the surface area of metal particles. The catalytic performances of Rh and Ir catalysts were hardly affected by a choice of a metal oxide support, while Pd and Pt catalysts showed different catalytic activity and selectivity depending on the metal oxide supports. This assortment is consistent with ability to dissociate NO depending on metals without the effect of any support materials. There, the metals to the left of Rh and Ir on the periodic table favor dissociation of NO and those to the right of Pd and Pt tend to show molecular adsorption of NO. Therefore, the catalytic property of noble metals could be assorted into two groups, i.e. Rh and Ir group whose own property would mainly dominate the catalytic performance, and Pd and Pt group whose interaction with metal oxides supports would clearly contribute to the reaction of NO with H₂. NO reduction activity of Pd and Pt was found to be promoted above that of Rh and Ir, provided that Pd and Pt were supported by CeO₂ and ZrO₂.     

The performance of iron-containing catalysts prepared at low temperature for carbon monoxide hydrogenation

The performance for carbon monoxide hydrogenation of amorphous- and crystalline-unsupported iron oxides following low temperature pretreatment in nitrogen, carbon monoxide and hydrogen has been examined. The phase compositions of the catalysts before and after catalytic evaluation have been determined by⁵⁷Fe Mössbauer spectroscopy. Pretreatment of amorphous non-potassium doped precipitates gave the formation of metallic iron catalysts which were catalytically active at low temperatures and which were shown by Mössbauer spectroscopy to be converted during evaluation to iron carbide and the iron oxide Fe₃O₄. Catalysts which were not pretreated were reduced during catalytic evaluation to Fe₃O₄. Pretreated potassium-doped catalysts composed of either iron carbide or a mixture of iron carbide and metallic iron gave hydrocarbon product distributions which showed a higher Schulz-Flory alpha value and a lower selectivity towards methane when the catalyst reached steady state as a result of an increase in carbon monoxide adsorption and/or a decrease in hydrogen adsorption. The used catalysts were shown by Mössbauer spectroscopy to contain iron carbide together with various proportions of metallic iron and the iron oxide Fe₃O₄. The activities of the pretreated amorphous and crystalline catalysts were comparable and may be related to the disintegration of the crystalline catalysts during pretreatment in carbon monoxide which induces the formation of particles with surface areas similar to those observed in the amorphous catalysts.     

Excimer laser processing of ZnO thin films prepared by the sol-gel process

ZnO thin films were prepared on soda-lime glass from a single spin-coating deposition of a sol-gel prepared with anhydrous zinc acetate [Zn(C₂H₃O₂)₂], monoethanolamine [H₂NC₂H₄OH] and isopropanol. The deposited films were dried at 50 and 300 °C. X-ray analysis showed that the films were amorphous. Laser annealing was performed using an excimer laser. The laser pulse repetition rate was 25 Hz with a pulse energy of 5.9 mJ, giving a fluence of 225 mJ cm⁻² on the ZnO film. Typically, five laser pulses per unit area of the film were used. After laser processing, the hexagonal wurtzite phase of zinc oxide was observed from X-ray diffraction pattern analysis. The thin films had a transparency of greater than 70% in the visible region. The optical band-gap energy was 3.454 eV. Scanning electron microscopy and profilometry analysis highlighted the change in morphology that occurred as a result of laser processing. This comparative study shows that our sol-gel processing route differs significantly from ZnO sol-gel films prepared by conventional furnace annealing which requires temperatures above 450 °C for the formation of crystalline ZnO.     

Electrodeposition of zinc oxide/tetrasulfonated copper phthalocyanine hybrid thin film for dye-sensitized solar cell application

Hybrid film of zinc oxide (ZnO) and tetrasulfonated copper phthalocyanine (TSPcCu) was grown on an indium tin oxide (ITO) glass by one-step cathodic electrodeposition from aqueous mixtures of Zn(NO₃)₂, TSPcCu and KCl. The addition of TSPcCu strongly influences the morphology and crystallographic orientation of the ZnO. The nanosheets stack of ZnO leads to a porous surface structure which is advantageous to further adsorb organic dyes. The photovoltaic properties were investigated by assembling the DSSC device based on both the only ZnO film and the ZnO/TSPcCu hybrid films. Photoelectrochemical analysis revealed that the optimized DSSC device with TSPcCu represented a more than three-fold improvement in power conversion efficiency than the device without TSPcCu. The DSSC based on ZnO/TSPcCu hybrid films demonstrates an open circuit voltage of 0.308 V, a short circuit current of 90 μA cm⁻², a fill factor of 0.26, and a power conversion efficiency of 0.14%.     

Characterization of the synthesis and reactivity behavior of nanostructured vanadia model catalysts using XPS and vibrational spectroscopy

Nanostructured vanadia model catalysts, i.e., highly dispersed vanadium oxide supported on mesoporous silica SBA-15 (VO_x/SBA-15), were prepared. The mechanism for the synthesis of VO_x/SBA-15 was elucidated by detailed characterization of the individual synthesis steps using XPS and vibrational spectroscopy. The resulting surface vanadium oxide species (0-2.3 V/nm²), grafted on the inner pores of the SBA-15 silica matrix, consists of tetrahedrally coordinated vanadia as inferred from UV-VIS- and Raman spectroscopy. The prepared vanadia model catalysts were tested in the partial oxidation of methanol to formaldehyde yielding high formaldehyde selectivities of 94% at 350 °C. XPS and Raman analysis of the catalyst after reaction reveal the presence of methoxy as well as a significant amount of carbonaceous species on the surface. Our results demonstrate that a detailed understanding of partial oxidation reactions requires the combination of complementary spectroscopic techniques ultimately within one experimental set-up.     

Formation and destruction of nitric oxide in methane flames doped with NO at atmospheric pressure

A study of formation and destruction of NO in adiabatic laminar premixed flames of CH₄ + O₂ mixtures diluted with N₂ or Ar (with various dilution ratios) in a range of equivalence ratios at atmospheric pressure is presented. Nitric oxide was seeded into the flames using mixtures of diluent gas + 100 ppm of NO. The heat flux method was employed to measure adiabatic burning velocities of these flames. Nitric oxide concentrations in the post-flame zone at 10, 15 and 20 mm above the burner surface were measured using probe sampling. Burning velocities and NO concentrations simulated using a previously developed chemical kinetic mechanism were compared with the experimental results. The conversion ratio of NO seeded into the flames was determined. The kinetic mechanism accurately predicts burning velocities over the range of equivalence ratios and NO conversion in the rich flames. Significant discrepancies between measured and calculated NO conversion in the lean and near-stoichiometric flames were observed and discussed.     

Electrical behaviour of catalytic nanostructured CeO2/CuOx composites under air-methane gas impulses

Nanostructured composites based on copper oxide and cerium dioxide phases [CuO-CeO₂] were elaborated from sol-gel route, with weight fractions of CuO phase ranging between 0 and 0.4. They are interesting potential catalysts allowing conversion of CH₄ and CO into CO₂ and H₂O and might be used in miniaturized gas sensors. An electrical study of this nanostructured system was carried out to determine catalytic behaviours under air-methane impulses at 350 °C. The electrical analysis was based on a specific homemade electronic device. Time dependent interactions between gas pulses and solid catalyst (CuO/CeO₂) were analyzed from a frequency modification of the electronic device. Kinetic parameters were determined from a model describing adsorption and desorption of gases adapted to short interaction time between gas and solid. These time dependent electrical behaviours were then correlated with infrared spectroscopy analyses allowing time dependent analysis of methane conversion into CO₂ gas, for long interaction time between gas and solid.     

Structure, morphology and optical properties of SiO2−x thin films prepared by plasma-assisted pulsed laser deposition

The amorphous silicon oxide SiO_2−x thin films were prepared by the plasma-assisted pulsed laser deposition (PLD) method. X-ray diffraction spectrometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-VIS-NIR scanning spectrophotometry and ellipsometry were used to characterize the crystallinity, microscopic morphology and optical properties of obtained thin films. The influences of substrate temperatures, oxygen partial pressures and oxygen plasma assistance on the compositions of silicon oxide (SiO_2−x) thin films were investigated. Results show that the deposited thin films are amorphous and have high surface quality. Stoichiometric silicon dioxide (SiO₂) thin film can be obtained at elevated temperature of 200 °C in an oxygen plasma-assisted atmosphere. Using normal incidence transmittance, a novel and simple method has been proposed to evaluate the value of x in transparent SiO_2−x thin films on a non-absorbing flat substrate.     

The state of the components in Cu-CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> catalysts for selective oxidation of CO

Cu-CeO₂ catalysts deposited on a commercial ZrO₂ support have been investigated. The catalyst composition has been optimized: the optimum copper content was found to be 5–10 wt % at a cerium oxide content of 23 wt %. The catalysts were investigated by X-ray diffraction analysis and X-ray photoelectron spectroscopy. According to the X-ray diffraction data, the support consists of the monoclinic ZrO₂ phase and cubic CeO₂ phase with an enlarged lattice parameter, while the catalysts contain CuO. The X-ray photoelectron data indicate the presence of a highly dispersed CuO₂ phase interacting with cerium oxide and zirconia on the surface of the catalyst having the optimum copper content.     

Alumina contribution to CO oxidation: A TPR and IR study

The alumina contribution to CO oxidation in the absence of O₂ on metal oxide supported catalysts was investigated by CO TPR and in-situ FTIR and DRIFT studies up to 800 °C. These tests were performed on two Al₂O₃ supported catalysts (1 wt.% Pt/La/γ-Al₂O₃ and 8 wt.% Cu/γ-Al₂O₃) and on two corresponding alumina supports (5 wt.% La₂O₃ stabilised γ-Al₂O₃ and high mechanical resistant spherical γ-Al₂O₃ particles). The quantitative determination of CO consumption and CO₂ and H₂ formation on the alumina supports was in agreement with a WGS reaction occurring between surface OH and CO with a predominantly 2:1 stoichiometry. In the CO TPR of metal oxide supported catalysts, in addition to the reduction of the metal, a WGS reaction took place with enhanced kinetics. This enhancement was the result of a CO spillover phenomenon from the metal to alumina hydroxyls. This phenomenon significantly affected the evaluation of the reduction degree of the supported metal and could not be neglected in the subsequent calculations.     

碱助剂促进Ni基催化剂氢解山梨醇制备二元醇

采用逐步湿浸渍的方法制备了一系列含有不同载体和碱促进剂的Ni基催化剂用于生物质基平台化合物山梨醇的氢解反应. 通过反应对载体和碱促进剂进行了筛选和组分含量的优化,碱性促进剂的引入不仅增强了催化剂的碱性,而且通过Ni²⁺和碱促进剂的强相互作用提高了Ni在催化剂上的分散性;10%Ni/10%La₂O₃/ZrO₂表现出了非常高的氢解活性和较好的二元醇(乙二醇和1,2丙二醇)选择性,金属Ni和碱促进剂La₂O₃之间的协同作用机理对于山梨醇选择性氢解制备二元醇影响显著. 在优化的反应条件下,山梨醇达到100%的转化并且有超过48%的二元醇产率. 研究中对催化剂进行了XRD、BET、H₂-TPR和CO₂-TPD表征,用于分析催化剂结构性能. 通过对山梨醇氢解以及中间产物动力学曲线的研究,得出多元醇氢解活性与所含羟基数正相关,产物的最终分布是氢解动力学平衡的最终结果.     

Flame synthesis of tungsten oxide nanostructures on diverse substrates

One-dimensional (1D) tungsten oxide nanostructures show great potential for applications in the areas of batteries, photoelectrochemical water-splitting, electrochromic devices, catalysts and gas sensors. 1D tungsten oxide nanostructures are currently synthesized by physical or chemical vapor deposition, which are limited by low temperatures, the need for vacuum conditions, frequently expensive catalysts, and difficulty in scaling up for mass-production. These limitations, however, can be overcome by flame synthesis. Here, using a co-flow multi-element diffusion burner, we demonstrate the atmospheric, catalyst-free, rapid, mild and scalable flame synthesis of diverse, quasi-aligned, large density, and crystalline tungsten oxide nanostructures on a variety of substrates. Specifically, under fuel-rich conditions, monoclinic 1D W₁₈O₄₉ nanowires and nanotubes were grown on tungsten, iron, steel and fluorinated tin oxide (FTO) substrates, with controlled diameters ranging from 10 to 400 nm and axial growth rates ranging from 2 to 60 μm/h. Monoclinic 1D WO₃ nanowires and nanotubes were grown, instead, on silicon and silicon dioxide substrates. Under fuel-lean conditions, diverse WO₃ nanostructures, including monoclinic 1D nanowires, cubic 2D nanobelts and monoclinic 3D nanocones were grown on tungsten and FTO substrates. The success of this versatile flame synthesis method is attributed to the large tunability of several synthesis parameters, including the flame stoichiometry, the tungsten source and growth substrate temperatures, the tungsten oxide vapor concentration, and the material of the growth substrate. This flame synthesis method can be extended to synthesize other 1D transition metal oxides as well, enabling many large-scale electronic and energy conversion applications.     

Fast degradation of dyes in water using manganese-oxide-coated diatomite for environmental remediation

By a simple wet-chemical procedure using a permanganate in the acidic medium, diatomite coated with amorphous manganese oxide nanoparticles was synthesized. The structural, microstructural and morphological characterizations of the as-synthesized catalysts confirmed the nanostructure of MnO₂ and its stabilization on the support - diatomite. The highly efficient and rapid degradation of methylene blue and methyl orange over synthesized MnO₂ coated Diatomite has been carried out. The results revealed considerably faster degradation of the dyes against the previously reported data. The proposed mechanism of the dye-degradation is considered to be a combinatorial effect of chemical, physicochemical and physical processes. Therefore, the fabricated catalysts have potential application in waste water treatment, and pollution degradation for environmental remediation.     

金属氧化物修饰对介孔纳米TiO2电极的染料敏化太阳能电池电化学性能的影响

将介孔TiO₂纳米粒子(m-TiO₂)多孔膜电极浸入相应的金属硝酸盐的500 oC热处理修饰金属氧化物(如Mg、ZnO、Al₂O₃或NiO).结果表明,金属氧化物修饰均可形成能垒对m-TiO₂膜电极的界面电荷传输过程产生影响,但外加偏压下其膜内电子传输和界面电荷复合均明显依赖于修饰氧化物的种类及其存在形态. 金属氧化物修饰的膜电极在电子传输和界面复合方面的变化与DSSCs的电流-电压特性曲线的变化规律具有明显的相关性,可不同程度地提高电池的光电压,而MgO、ZnO和NiO修饰的电池效率分别提高了23%、13%和6%. 上述结果表明调控电池的本征参数可以改善TiO₂-基DSSCs的性能.