Size and support effects for CO oxidation on supported Pd catalysts

Science China Chemistry - Supporting Pd catalysts characterized significant different size distribution were obtained using PdCl2, [Pd(NH3)4](NO3)2 and Pd(acac)2 as precursors. High-resolution...     

Microwave synthesis of supported Au and Pd nanoparticle catalysts for CO oxidation

We report the microwave synthesis and characterization of Au and Pd nanoparticle catalysts supported on CeO2, CuO, and ZnO nanoparticles for CO oxidation. The results indicate that supported Au/CeO2 catalysts exhibit excellent activity for low-temperature CO oxidation. The Pd/CeO2 catalyst shows a uniform dispersion of Pd nanoparticles with a narrow size distribution within the ceria support. A remarkable enhancement of the catalytic activity is observed and directly correlated with the change in the morphology of the supported catalyst and the efficient dispersion of the active metal on the support achieved by using capping agents during the microwave synthesis. The significance of the current method lies mainly in its simplicity, flexibility, and the control of the different factors that determine the activity of the nanoparticle catalysts.     

Cu-Co-Fe oxide catalysts supported on carbon nanotubes for the oxidation of CO

The catalytic activity and adsorption characteristics of the surface of catalysts in the form of carbon nanotubes produced on nickel and cobalt oxides with the Cu-Co-Fe oxide system as supported active phase were studied. At carbon nanotubes produced on nickel oxide with (10 + 10) wt.% of the catalytically active phase total conversion of CO to CO₂ is realized at 47 °C. This sample has high specific surface area and a large volume of mesopores. It was shown that the increase in catalytic activity correlates with the increase in the amount of the α₂ form of CO₂. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 4, pp. 222–226, July–August, 2006.     

Kinetics of lactose and rhamnose oxidation over supported metal catalysts

Several mono- and bimetallic Pd, Pt, Rh and Ru supported on alumina and active carbon catalysts were characterized by CO chemisorption, nitrogen adsorption, XPS and XRD and acidity titrations were performed for active carbon supported catalysts. These catalysts were tested in oxidation of two sugars, namely lactose and rhamnose, at 60 °C and at 70 °C under slightly alkaline conditions (pH 8) with molecular oxygen. The results revealed that there is an optimum metal particle size in a range of 3-10 nm giving the highest initial TOFs for both oxidations. Furthermore, the catalytic activities and conversions were related to other catalyst properties, such as the type and amount of promoters and the presence of different phases. In situ catalyst potential measurements revealed that there is an inverse correlation between the increase of catalyst potential as a function of sugar conversion and the catalyst activity after prolonged reaction times. This method is a valuable tool for in situ characterization of catalysts correlating well with their activities.     

Surface reorganization of carbon supported cobalt catalysts during CO chemisorption

Different monometallic catalysts containing Fe, Co or Ni and a Fe–Co bimetallic catalyst have been prepared by impregnation of an activated carbon. The formation of subcarbonyl species during CO adsorption, as detected by the slow adsorption rate, was observed. From the CO adsorption isotherms, the possibility of a surface reorganization in the Co catalysts induced by the interaction with CO is deduced.

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, Fe, Co Ni Fe–Co . CO . Co , CO.

     

The study of the active surface for CO oxidation over supported Pd catalysts

CO oxidation was investigated on various powder oxide supported Pd catalysts by temperature-programmed reaction.The pre-reduced catalysts show significantly higher activities than the pre-oxidized ones.Model studies were performed to better understand the oxidation state,reactivities and stabilities of partially oxidized Pd surfaces under CO oxidation reaction conditions using an in situ infrared reflection absorption spectrometer(IRAS).Three O/Pd(100)model surfaces,chemisorbed oxygen covered surface,surface oxide and bulk-like surface oxide,were prepared and characterized by low-energy electron diffraction(LEED)and Auger electron spectroscopy(AES).The present work demonstrates that the oxidized palladium surface is less active for CO oxidation than the metallic surface,and is unstable under the reaction conditions with sufficient CO.     

SBA-16负载金属氧化物催化剂合成、表征及催化CO氧化反应活性

将V2O5, CeO2和CuO分散到提取自稻米壳的SBA-16上,考察了其催化CO氧化反应活性,并采用X射线衍射、扫描电镜、透射电镜、程序升温还原和紫外漫反射光谱对所制催化剂进行了表征。结果表明,掺杂CuO的介孔氧化硅是一种有前景的催化剂,其CO转化率可达98%以上。     

Supported metal catalysts based on fibrous carbon material for low-temperature CO oxidation

A number of supported-metal (Pt, Pd) catalysts based on Karbopon nonwoven carbon fibers were prepared by deposition from hydrosols and by ion exchange. The catalytic activity of the catalysts in low-temperature oxidation of carbon monoxide by atmospheric oxygen was determined. Catalyst samples were studied by transmission electron microscopy.     

Effective platinum catalysts for low-temperature oxidation of CO

A number of platinum-based catalysts bonded on carbon fiber karbopon were prepared using alcohol solutions of H₂PtCl₆. The catalytic activity of the samples was determined in the low-temperature oxidation of carbon monoxide by oxygen. The effect of the solvent nature of the precursor on the activity of the catalysts was determined. The best results were obtained in the presence of 1.5% Pt/karbopon catalyst prepared using isobutyl alcohol; 100% CO conversion was achieved in respiratory treatment (12000 h^?1, room temperature).     

Enhanced CO photocatalytic oxidation in the presence of humidity by tuning composition of Pd-Pt bimetallic nanoparticles supported on TiO2

Here we put forward for the first time that the negative effect of humidity on CO photooxidation at room temperature can be overcome by adjusting the composition of Pd-Pt bimetallic particles supported on TiO(2). Consequently, optimized Pd(x)Pt(1-x)/TiO(2) materials can be considered as common and efficient photocatalysts for simultaneous elimination of CO and VOCs in the presence of humidity, i.e. for real indoor air treatment.     

REFeO~3上CO氧化Redox机理的控制步骤

用柠檬酸配合法制备REFeO~3 (RE=la, Pr, Nd, Sm, Eu, Gd, 及Dy)。用XRD测定了REFeO~3的钙钛矿结构。用CO还原脉冲及O~2氧化脉冲证实REFeO~3上CO氧化为Redox机理。用外循环流动无梯度反应器研究CO氧化稳态动力学。动力学方程中的参数用正交设计法估计。催化剂用CO还原的速率常数k~1比还原了的催化化剂用O~2再氧化速率常数k~2要大, k~1/k~2值在4.22～133之间, 这说明在REFeO~3上CO氧化的控制步骤为还原催化剂的再氧化。用脉冲法得到的CO转化率(X~C~O)比O~2的转化率(X~O~2)要大。脉冲法证实稳态动力学控制步骤的结论。Redox动力学方程式(9)可简化为控制步骤方程式(11)。催化剂还原速度常数与一定P~C~O及P~O~2下的反应速度呈近似的线性关系。在REFeO~3上CO氧化存在补偿效应。     

Application of anionic micelle for dramatic enhancement in the quenching-based metal ion fluorosensing

We introduce a simple and efficient strategy to enhance the efficiency of a quenching-based fluorosensor for metal ions by several orders of magnitude by using commercially available anionic surfactants varying hydrophobic chain length. Anionic surfactants with a proper choice of hydrophobic chain length at their optimum concentrations are efficient to boost up the efficiency of copper ion sensor dramatically. This simple and convenient strategy is, in general, applicable to quenching-based fluorosensors, new or established, in aqueous solution. It is powerful enough to transform a virtually non-sensor fluorophore to a sensor with a commendable efficiency with the help of proper surfactant. Thus, in this communication, light has been thrown on the application of surfactants toward increasing fluorosensing efficiency of a quenching based sensor.     

植物还原法制备负载型金纳米催化剂催化乙醇选择氧化反应

采用侧柏叶提取液还原氯金酸制备负载型金纳米催化剂,通过乙醇选择氧化反应,筛选出催化性能较好的TiO2载体。以TiO2载体为载体,考察了Au负载量、焙烧温度、催化剂用量、碳酸氢钠添加量及催化剂反应条件(时间、温度、压力)等因素对乙醇选择氧化反应的影响。结果表明,1.5%Au/TiO2催化剂(Au负载量为1.5%,质量分率,下同)催化乙醇选择氧化反应性能最佳,产物为乙醛、乙酸乙酯和缩醛,0.5%碳酸氢钠添加剂可抑制缩醛的生成,并可显著提高乙醇转化率和乙酸乙酯选择性。通过优化催化反应条件(1.5%Au/TiO2催化剂焙烧温度为400℃、用量为0.4 g、反应温度为100℃、氧气压力为3 MPa、反应时间为3 h时),乙醇转化率为47.9%,乙酸乙酯选择性为89.1%。     

Synthesis of silica supported AuCu nanoparticle catalysts and the effects of pretreatment conditions for the CO oxidation reaction

Supported gold nanoparticles have generated an immense interest in the field of catalysis due to their extremely high reactivity and selectivity. Recently, alloy nanoparticles of gold have received a lot of attention due to their enhanced catalytic properties. Here we report the synthesis of silica supported AuCu nanoparticles through the conversion of supported Au nanoparticles in a solution of Cu(C(2)H(3)O(2))(2) at 300 °C. The AuCu alloy structure was confirmed through powder XRD (which indicated a weakly ordered alloy phase), XANES, and EXAFS. It was also shown that heating the AuCu/SiO(2) in an O(2) atmosphere segregated the catalyst into a Au-CuO(x) heterostructure between 150 °C to 240 °C. Heating the catalyst in H(2) at 300 °C reduced the CuO(x) back to Cu(0) to reform the AuCu alloy phase. It was found that the AuCu/SiO(2) catalysts were inactive for CO oxidation. However, various pretreatment conditions were required to form a highly active and stable Au-CuO(x)/SiO(2) catalyst to achieve 100% CO conversion below room-temperature. This is explained by the in situ FTIR result, which shows that CO molecules can be chemisorbed and activated only on the Au-CuO(x)/SiO(2) catalyst but not on the AuCu/SiO(2) catalyst.     

Liquid-phase oxidation of benzothiophene and dibenzothiophene by cumyl hydroperoxide in the presence of catalysts based on supported metal oxides

The liquid-phase oxidation of benzothiophene and dibenzothiophene by cumyl hydroperoxide in the presence of supported metal oxide catalysts was carried out in octane in an N₂ atmosphere at 50–80°C. The cumyl hydroperoxide, benzothiophene, and dibenzothiophene conversions and the yield of sulfones were determined for catalysts of various natures. In the presence of MoO₃/SiO₂, the most efficient and most readily regenerable catalyst, the benzothiophene conversion was ～60% and the dibenzothiophene conversion was as high as 100% upon almost complete consumption of cumyl hydroperoxide. The influence of unsaturated and aromatic compounds (oct-1-ene, toluene) on the catalytic effect was studied. The kinetics of substrate oxidation and cumyl hydroperoxide decomposition and an analysis of the cumyl hydroperoxide conversion products suggested a benzothiophene and dibenzothiophene oxidation mechanism including the formation of an intermediate complex of the hydroperoxide with the catalyst and the substrate and its transformation via heterolytic and homolytic routes.     

Crystallite size determination for supported metal catalysts by single X-ray profile fourier analysis

An X-ray diffraction method is presented capable of determining the average particle size, microstrains, the probability of faults as well as a particle size distribution function in crystalline materials. The method is based on the Fourier analysis of a single X-ray diffraction profile. Results obtained on supported platinum catalysts used in H/D isotopic exchange reactions are reported. On the basis of experimental spectra and our XRLINE1 code all structural parameters could be obtained.     

Crystallite size determination for supported metal catalysts by single X-ray profile fourier analysis

An X-ray diffraction method is presented capable of determining the average particle size, microstrains, the probability of faults as well as a particle size distribution function in crystalline materials. The method is based on the Fourier analysis of a single X-ray diffraction profile. Results obtained on supported platinum catalysts used in H/D isotopic exchange reactions are reported. On the basis of experimental spectra and our XRLINE1 code all structural parameters could be obtained.