Kinetic model ofCO oxidation on a nonuniform surface analyzed with regard toCOads spillover, III. Homotopic method. Effect of the reaction mixture composition

Homotopic method has been used to analyze the kinetic model of three-stageCO oxidation on two nonuniform surface patches conjugated byCO _ads spillover. The diagrams of steady states depending onP(CO) at various temperatures have been built.CO _ads spillover from one patch to another changes substantially the bifurcation picture of the steady states.     

Kinetic model ofCO oxidation on nonuniform surface analyzed regardingCOads spillover, 2. homotopic method. Effect ofm1 surface portion

The homotopic method has been used to analyze the kinetic model of three-stageCO oxidation on two nonuniform surface patches conjugated byCO ₂ spillover. Diagrams of steady states depending on the portion of surface patchm ₁ at various temperatures and pressure ratiosP(O ₂)/P(CO) have been constructed. The ratios of different type patches corresponding to the maximum overall reaction rate have been found.     

CO oxidation over the Pt-Rh system. 3. Reaction on a heterophase surface

The reaction of the CO oxidation over a Pt-Rh heterophase surface, which represents 10-20 nm platinum particles located on a rhodium film, which in turn is deposited on an inert support, has been investigated at low pressures (P < 2'10^-5 mbar). The results are compared with the data for the clean surfaces of Pt and Rh. In the high-temperature range, the rate of CO₂ formation on the heterophase surface is found to be higher than the sum of the rates on individual metals corrected by the surface area of the different metals. The nature of the synergistic effect in the CO oxidation is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetics of CO oxidation on the surface of heterophase catalysts. Modeling by the Monte Carlo method

The Monte Carlo method has been used to simulate CO oxidation on a lattice consisting of various alternating patches: M1, where s(CO)>s(O₂) and M2, where s(CO)2). The reaction is shown to proceed over all the surface at low temperature as CO_ads spillover from M1 to M2 and backwards.     

COads spillover and low-temperature activity of heterophase catalysts in CO oxidation

The kinetics of CO oxidation on heterophase surfaces composed of two different types of patches M1 and M2 is analyzed. The kinetic conjugation of the patches caused by CO_ads spillover leads to the substantial change in reaction rate temperature dependences, as well as to the appearance of a low-temperature, superadditive activity.     

Pt-表层限域的表面FeOx结构用于低温CO氧化反应

通过简单的浸渍-还原并随后在酸性溶液中处理制备了Pt-Cu双金属催化剂. 利用电感耦合等离子体发射光谱、X射线衍射和X射线光电子能谱对不同处理条件下的Pt-Cu纳米粒子的结构和组成进行了表征. 研究发现, Pt-Cu催化剂在高温H₂中还原形成了PtCu₃合金结构, 酸洗处理后形成了包含Pt-骨架(Pt-skeleton)的表面结构和PtCu₃合金核的纳米粒子. 而Pt-骨架结构又可通过在H₂中退火转变为规整的Pt-表层(Pt-skin)结构. Pt-表层表面修饰Fe氧化物后在CO选择氧化反应中表现出较好的催化性能. 通过此方法制备的三金属Pt-Cu-Fe催化剂可达到与Pt-Fe相近的高活性, 并且催化剂中Pt的用量大大降低.     

Modeling of CO oxidation rate oscillations on a chain of surface patches

Autooscillations of CO oxidation rate are considered for a surface, which is a chain of uniform M1–M4 patches differing by their properties. For chain 5333 due to CO_ads diffusion, induced oscillations propagate from oscillating patches M1 (scheme 5) to patches M2–M4 (Scheme 3), which themselves do not sustain the oscillation mode.     

Kinetics of low temperature CO oxidation over Pt/SnO2 catalyst

In a CO−O₂ stoichiometric mixture, the kinetic parameters, reaction order, rate constant and activation energy of CO oxidation over a Pt/SnO₂ catalyst have been measured using a fixed bed flow reactor near 0°C. The results show that it is a first-order reaction. The activation energy of CO oxidation over Pt/SnO₂ prepared with SnO₂ calcined at 300°C was approximately 21 kJ/mol. The activation energy of CO oxidation over Pt/SnO₂ changed slowly with SnO₂ calcination temperature above 400°C, and reached approximately 45 kJ/mol.     

表面活性剂模板法制备CeO_2/CuO催化剂用于富氢气氛中CO优先氧化

采用表面活性剂模板法合成了一组不同配比的CeO2/CuO催化剂,使用高分辨透射电子显微镜(HRTEM)、X射线粉末衍射(XRD)、N2吸附脱附和程序升温还原(H2-TPR)等测试手段对催化剂进行了表征,并对其在富氢气氛中CO优先氧化的催化性能进行了研究。结果表明,立方相萤石结构的氧化铈颗粒粒径在4 nm左右,它们聚集成小簇后分散在块状氧化铜的表面;从粒径分布来看所制备的催化剂是逆负载型催化剂。催化性能测试结果显示,CeO2/CuO催化剂中有两种类型吸附位的存在,即由CuO提供的化学吸附位和由氧化铈提供的氧空位,而界面处两种类型吸附位的共存促进了CO的优先氧化。     

焙烧温度对Pd-Cu/凹凸棒土CO常温催化氧化性能的影响

以凹凸棒土(APT)作载体,采用等体积浸渍法制备了Pd-Cu/APT催化剂,以CO氧化为探针反应,在连续流动微反装置上,考察了焙烧温度对催化剂CO常温催化氧化性能的影响。通过N2-物理吸附、XRD、TG、FT-IR和H2-TPR等手段对催化剂的结构和性质进行了表征。结果表明,随焙烧温度升高,Pd-Cu/APT中载体逐步脱水,进而引起催化剂结构和织构变化,其中,Cu物种由Cu(OH)Cl逐渐向CuO转变,同时,高分散的Pd物种与Cu物种间相互作用先增强后减弱。经300℃焙烧的催化剂比表面积大,Cu物种以Cu(OH)Cl形式存在,且具有良好的分散状态,与Pd物种之间产生较强的相互作用,显著提高了其还原性能。在空速6 000 h-1、CO体积分数0.5%、水蒸气体积分数3.3%的反应条件下,常温可将CO完全转化800 min以上。焙烧温度高于或低于300℃均引起CO常温催化氧化性能的下降。     

Effects of reduction temperature and content of Pd loading on the performance Pd/CeO2 catalyst for CO oxidation

Palladium nanoparticles were prepared by thermally assisted reduction using glutathione as reduction agent. The Pd loading on CeO₂ for CO oxidation was optimized to 1.5 wt%. The catalysts reduced at 350 C show the highest activity for CO oxidation, which achieve 100% CO conversion at 70℃.     

Low temperature CO oxidation on Au/TiO2 sol-gel catalysts

A comparative study on Au/TiO₂catalysts prepared by impregnation with HAuCl₄of commercial TiO₂ or by impregnation of sol-gel derived TiO₂has been carried out during CO oxidation. Specific surface areas and mean Au particle of 49 and 74 m²/g and 35 and 25 Å were obtained for impregnated commercial TiO₂ and sol-gel preparations, respectively. XRD patterns shown that in sol-gel derived TiO₂ only anatase phase was identified, while in commercial TiO₂ anatase and rutile phases co-exist. Titania support effect on Au activity for the oxidation of CO has been observed. The light-off during the reaction on Au/TiO₂initiates at 50°C, whereas for commercial impregnated TiO₂ catalyst the light-off initiates at 200°C.     

Kinetic features of the steady state photocatalytic CO oxidation by air on TiO2

The paper reports quantum efficiency dependence of the steady state gas phase photocatalytic oxidation of CO over dispersed anatase on CO and CO₂ concentrations, temperature and UV light intensity. A tentative mechanism of the process is proposed.     

Zirconia supported La, Co oxides and LaCoO3 perovskite: structural characterization and catalytic CO oxidation

ZrO₂-supported La, Co oxide catalysts with different La, Co loading (2, 6, 8, 12 and 16 wt.% as LaCoO₃) were prepared by impregnation of tetragonal ZrO₂ with equimolar amounts of La and Co citrate precursors and calcination at 1073 K. The catalysts were characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and BET specific surface area determination. Catalytic CO oxidation was performed at 298–800 K. XRD revealed the presence of tetragonal zirconia with traces of the monoclinic phase. LaCoO₃ perovskite was also detected for loading higher than 6%. XAS experiments suggested that at high loading LaCoO₃ and Co₃O₄ were formed, while at low loading, La, Co oxide species interacting with support, and hard to be structurally defined, prevailed. The catalysis study evidenced that the catalytic activity was due to segregated and highly dispersed cobalt oxide species.     

Catalytic properties of LnSrCoO4 (Ln = La, Sm) in the oxidation of CO and C3H8

Perovskite-like LnSrCoO₄(Ln=La, Sm) mixed oxides of K₂NiF₄ structure were synthesized by the polyglycol gel method and used successfully for CO and C₃H₈ oxidation for the first time. The structure was characterized by means of XRD, TEM, BET, O₂-TPD and CO₂-TPD, respectively. An oxidation mechanism over LnSrCoO₄is proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of promoters on the performance of Au/MnOx and Pt/SnOx/SiO2 low-temperature CO oxidation catalysts

The influence of promoters on Pt/SnO_x/SiO₂ and Au/MnO_x low-temperature CO oxidation catalysts has been investigated under stoichiometric reaction conditions with no CO₂ added to the feed gas. The performance of Pt/SnO_x/SiO₂ catalysts is improved significantly by the addition of 1 wt.% Fe but reduced by the addition of 5 wt.%Fe, 1 wt.% Sb, 5 wt.% Sb, 1 wt.% As, 5 wt.%As and 1.8 wt.% P. The performance of Au/MnO_x is improved significantly by the addition of 1 at.% Ce but reduced by the addition of 1 at.% Co. For the catalysts and conditions examined, the Au/MnO_x catalysts are superior to the Pt/SnO_x/SiO₂ catalysts with respect to both activity and decay characteristics.     

Canard explosion and internal signal stochastic bi-resonance in the CO oxidation on platinum surface

Canard explosion means a dramatic change fromsmall amplitude quasi-harmonic oscillation to largeamplitude relaxation oscillation, accompanied by anexponential increase of period, of a limit cycle withina very narrow interval of a control parameter. Thisphenomenon was first found in the Van Der Pol equa-tions[1], and later has been found also in chemical[2]and biological[3] systems. Generally speaking, it is theresult of multi-time scales in the system, and can bedealt with singular perturbati…     

CTAB assisted hydrothermal synthesis, controlled conversion and CO oxidation properties of CeO2 nanoplates, nanotubes, and nanorods

In this work, CeO₂ nanoplates were synthesized by a hydrothermal reaction assisted by hexadecyltrimethylammonium bromide (CTAB) at 100-160 °C. The size of nanoplates was around 40 nm. Further experiment showed that the controlled conversion of nanoplates into nanotubes, and nanorods can be realized by changing the reaction time, temperature, and CTAB/Ce³⁺ ratio value. X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption measurements were employed to characterize the samples. The CO oxidation properties of nanorods, nanoplates, and nanotubes were investigated. An enhanced catalytic activity has been found for CO oxidation by using CeO₂ nanoplates as compared with CeO₂ nanotubes and nanorods, and the crystal surfaces (100) of CeO₂ nanoplates were considered to play an important role in determining their catalytic oxidation properties.     

CO在Pd平板与Pd38团簇表面上的催化氧化机理研究

采用密度泛函理论(DFT)计算模拟Pd平板和Pd_(38)团簇上的CO催化氧化过程,分析了CO在Pd催化剂表面上的氧化反应机理。结果表明,在Pd_(38)团簇模型上CO催化氧化的决速步骤是O_2的解离,反应能垒为0.65 eV,而在Pd平板模型上的决速步骤是CO的氧化,其反应能垒为0.87 eV。对比决速步骤的活化能发现,CO在Pd_(38)团簇上的氧化反应更易进行,说明CO氧化更易在小颗粒催化剂表面上进行,即Pd催化剂的活性与活性组分颗粒大小相关,活性组分颗粒越小,暴露的活性位点越多,其催化活性也越高。     

单晶Au表面和Au/TiO2（110）模型催化剂表面CO氧化反应机理和活性位

在分子尺度上介绍了Au/TiO2(110)模型催化剂表面和单晶Au表面CO氧化反应机理和活性位、以及H2O的作用.在低温(<320 K), H2O起着促进CO氧化的作用, CO氧化的活性位位于金纳米颗粒与TiO2载体界面(Auδ+–Oδ––Ti)的周边. O2和H2O在金纳米颗粒与TiO2载体界面边缘处反应形成OOH,而形成的OOH使O–O键活化,随后OOH与CO反应生成CO2.300 K时CO2的形成速率受限于O2压力与该反应机理相印证.相反,在高温(>320 K)下,因暴露于CO中而导致催化剂表面重组,在表面形成低配位金原子.低配位的金原子吸附O2,随后O2解离,并在金属金表面氧化CO.