PREPARATION OF Au/SULFONATED POLYSTYRENE CATALYSTS FOR LOW-TEMPERATURE CO OXIDATION*

Supported An catalysts for low-temperature CO oxidation were prepared by solvated motal atom impregnation(SMAI) and conventional impregnation (CI). X-ray photoelectron spectroscopy (XPS) investigations indicated that theelemental gold in all the samples was in the metallic state. XRD measurements showed that the mean diameters of Auparticles prepared by SMAI were smaller than those prepared by CI with the same gold content. Catalytic tests showed thatthe SMAI catalyst had higher CO oxidation activity than the CI catalyst with the same compositions. Both SMAI and CIcatalysts exhibited high activity in low temperature CO oxidation. Full CO conversion was obtained at 323--383K.     

固相浸渍法和湿浸渍法制备CuO/CeO2催化剂及其CO氧化性能的对比研究

采用固相浸渍法和常规湿浸渍法制备了一系列CuO/CeO₂催化剂,并结合X射线衍射（XRD）、氢气-程序升温还原（H₂-TPR）、激光拉曼光谱（LRS）、原位漫反射红外光谱（in situ DRIFTS）、X射线光电子能谱（XPS）等手段考察了制备方法对催化剂结构性质及其在CO氧化反应中性能的影响. XPS和H₂-TPR结果表明,固相浸渍法更有利于得到高分散的铜物种,并促进CuO物种的还原. LRS结果表明,相比于湿浸渍法,固相浸渍法能产生更多氧空位,而这些氧空位可以活化参与反应的O₂. CO氧化活性测试结果表明,当铜负载量相同时,固相浸渍法制备的催化剂相比于湿浸渍法表现出更好的催化性能. 结合多种表征结果发现,催化剂CO氧化性能与其表面氧空位和Cu⁺-CO浓度紧密相关,提出了CuO/CeO₂催化剂在CO氧化反应中可能的协同作用机制.     

固相浸渍法制备NiO/CeO2催化剂及其在CO氧化反应中的应用

采用固相浸渍法制备了一系列NiO/CeO2催化剂,并通过与常规湿浸渍法比较,考察了制备方法对催化剂和CO氧化反应性能的影响.同时结合X射线衍射(XRD),N2吸附-脱附(BET),透射电镜(TEM),氢气-程序升温还原(H2-TPR),拉曼(Raman)光谱,X射线光电子能谱(XPS)等手段对催化剂的结构和表面物种分散状态进行了表征.CO氧化活性测试结果表明,当镍负载量相同时,固相浸渍法制备的催化剂相比于湿浸渍法表现出更好的催化性能.TEM、XPS、H2-TPR结果表明,固相浸渍法更有利于加强镍铈间的相互作用和得到高分散的镍物种,从而促进镍物种的还原.Raman结果表明固相浸渍法相比于湿浸渍法能产生更多氧空位,这有利于氧气在催化剂表面的活化,使得CO氧化反应更容易进行.     

SMAI和CI法制备的Ni—Ag／SiO2催化剂的结构与催化性质研究

应用溶剂化金属原子浸渍（ＳＭＡＩ）法和普通浸渍（ＣＩ）法制备了金属含量相同的ＳｉＯ２负载Ｎｉ－Ａｇ双金属催化剂。ＸＲＤ和磁测定结果表明ＳＭＡＩ催化剂中Ｎｉ和Ａｇ的粒度均小于金属含量相同的ＣＩ催化剂，ＳＭＡＩ催化剂中Ｎｉ和Ａｇ未形成合金，而ＣＩ催化剂中Ｎｉ和Ａｇ形成了合金。ＳＭＡＩ和ＣＩ催化剂都具有超顺磁性。研究了这些催化剂在甲苯加氢反应的催化性质，结果表明与组成相同的普通浸渍法催化相比，ＳＭＡＩ催     

Effect of oxygen mobility in the lattice of Au/TiO<Subscript>2</Subscript> on formaldehyde oxidation

Two Au catalysts supported on TiO₂ were prepared by impregnation method followed by sodium borohydride reduction or calcination in air (Au/TiO₂-R and Au/TiO₂-C, respectively). The 1 wt % Au/TiO₂-R sample was found to be highly efficient for the oxidation of low concentrated formaldehyde at room temperature. A HCHO conversion of 98.5% was achieved with this catalyst, whereas the Au/TiO₂-C sample showed almost no activity under the same conditions. Highly dispersed metallic Au nanoparticles with small size (∼3.5 nm) were identified in the 1 wt % Au/TiO₂-R catalyst. A significant negative shift of Au4f peak in XPS spectra with respect to bulk metallic Au was observed for the 1 wt % Au/TiO₂-R but no similar phenomena was found for the heat-treated catalyst. More Au nanoparticles and higher content of surface active oxygen were identified on the surface of the Au/TiO₂-R in comparison with the Au/TiO₂-C, suggesting that the Au/TiO₂-R catalyst can enhance the amount of active sites and species involved in for HCHO oxidation. The reduction treatment by sodium borohydride promotes the formation of dispersed metallic Au nanoparticles with small size because it facilitates the electron transfer and increases the content of surface Au nanoparticles and activated oxygen. All these factors are responsible for a high activity of this catalyst in the oxidation of HCHO.     

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.     

Oxidation of Carbon Monoxide over Cu/CeO_2 Catalysts Prepared by SMAI

Introduction Carbon monoxide is ubiquitous air pollutants emitted by many sources. Total oxidation of carbon monoxide to carbon dioxide is employed to meet environmental regulations in an economic way. Precious metals (Pt, Pd) are well-known oxidation catalysts with high activity and stability, and are widely used for exhaust gas emission control. However, the high cost of precious metals and their sensitivity to sulfur poisoning have long motivated the search for substitute catalysts. …     

溶剂化金属原子浸渍法制备高分散负载型催化剂——ⅩⅣ.Pd催化剂的表面组成及CO_2甲烷化催化性能

用元素分析、热脱附和H_2还原脱附等方法分析了Pd/γ-Al_2O_3、Pd/MgO、Pd/TiO_2溶剂化金属原子浸渍(SMAI)催化剂的表面组成和孔结构。结果表明Pd颗粒表面覆盖着一些有机碎片,这些碎片主要由C_1和少量C_2,C_3及C_3以上物种组成。SMAI催化剂的比表面积均高于相应纯载体的比表面积。而平均孔径均小于后者,CO_2甲烷化反应中,SMAI催化剂的活性均高于相应的普通浸渍法(CI)催化剂,而活化能却低于后者。在SMAI催化剂上CO_2甲烷化反应机理与Solymosi机理相同。     

聚合物固载Co-Pd 催化剂的结构与活性

采用溶剂化金属原子浸渍(SMAI)法制备了几种不同金属含量的Co Pd催化剂,用X射线衍射、X射线光电子能谱和磁测定对催化剂进行表征,并与普通浸渍法(CI)制得的相同金属含量的催化剂进行比较.结果表明SMAI法制备的催化剂金属粒度小于CI法制备的催化剂,且前者零价金属含量高于后者.SMAI法制备的催化剂Co在表面上富集,而CI法制备的催化剂Co在表面和体相的金属含量基本相同.在二丙酮醇加氢及电催化反应中, SMAI法催化剂比相同组成的CI法催化剂具有更高的催化活性.     

Influence of the addition of Pd and Cu to cobalt catalysts prepared by SMAI for F-T synthesis

The Co-Pd/SiO₂ and Co-Cu/SiO₂ catalysts were prepared via solvated metal atom impregnation (SMAI) method and investigated for the Fischer-Tropsch (F-T) synthesis. The catalysts contained 5wt.% Co and a weight ratio of Pd (or Cu) to Co of 1/30. XPS indicated that Co, Pd and Cu were in metallic state. The results of XPS and magnetic measurements showed that Co and Pd (Cu) were alloyed. The Co particles on the catalysts were very highly dispersed and they displayed superparamagnetic behavior. FT-IR indicated that the electrons shifted from Cu and Pd to Co. Catalytic tests showed that CO hydrogenation rates followed the order Pd-Co > Cu-Co > Co.      

CuO Catalysts Supported on Porous TiO2 Microspheres for Low-Temperature CO Oxidation

The porous TiO₂ microspheres were prepared by the reversed-phase suspension polymerization and sol-gel method using reversed-phase suspension droplets as the templates. The CO oxidation catalytic properties of the CuO/TiO₂ catalysts prepared by hydrothermal method and impregnation method were extensively investigated. The structure of CuO/TiO₂ catalysts was determined by TG-DTA, XRD, TEM, and XPS. The results indicated that the redox capacity of CuO/TiO₂ was greatly depended on the aqueous solution concentration of Cu(NO₃)₂ used in the preparation of CuO/TiO₂ and the calcination temperature of the CuO/TiO₂ catalysts.     

Catalytically Active Rh Sub‐Nanoclusters on TiO2 for CO Oxidation at Cryogenic Temperatures

The discovery that gold catalysts could be active for CO oxidation at cryogenic temperatures has ignited much excitement in nanocatalysis. Whether the alternative Pt group metal (PGM) catalysts can exhibit such high performance is an interesting research issue. So far, no PGM catalyst shows activity for CO oxidation at cryogenic temperatures. In this work, we report a sub‐nano Rh/TiO₂ catalyst that can completely convert CO at 223 K. This catalyst exhibits at least three orders of magnitude higher turnover frequency (TOF) than the best Rh‐based catalysts and comparable to the well‐known Au/TiO₂ for CO oxidation. The specific size range of 0.4–0.8 nm Rh clusters is critical to the facile activation of O₂ over the Rh–TiO₂ interface in a form of Rh?O?O?Ti (superoxide). This superoxide is ready to react with the CO adsorbed on TiO₂ sites at cryogenic temperatures.     

Preparation of supported gold nanoparticles by a modified incipient wetness impregnation method

In this work, we show that if the mere procedure of impregnation of oxide supports with chloroauric acid, which is well-known to lead to large gold particles, is followed by a step of washing with ammonia, small gold particles (3-4 nm) can be obtained after a treatment of calcination at 300 degrees C on any type of oxide supports (alumina, titania, silica). Moreover, gold leaching is very limited during the washing step, and a large range of gold loadings (0.7-3.5 wt %) can be achieved. Elemental analysis, Raman spectroscopy, and temperature programmed desorption under argon show that this ammonia posttreatment results in the removal of chloride ligands from the coordination sphere of Au(III) precursor and their replacement by ammine ligands, leading to an ammino-hydroxo or an ammino-hydroxo-aquo gold complex and not to gold hydroxide. The Au/TiO(2) catalysts prepared with this modified procedure of impregnation are almost as active as those prepared by deposition-precipitation with urea in the CO oxidation reaction performed at room temperature.     

Au/Al2O3催化剂的制备及其在CH4/CO2重整反应中的催化活性

采用浸渍法和沉积－沉淀法制备了四种不同的Au/Al2O3催化剂，测定了它们在氢气还原前后及催化反应后的金含量及比表面积，结果表明，制备方法明显影响催化剂的金含量，应用X－光粉末衍射技术研究了这些催化剂经还原处理及反应后的物相变化，金以Au^0物相存在，没有发现氧化态的金物相，考察了该催化剂在CH4／CO2重整反应中的催化活性，发现金催化剂的活性取决于金粒子的大小，浸渍法制备的金催化剂具有较大的金晶粒尺寸，催化活性低，沉积－沉淀法制备的金催化剂金晶粒尺寸较小，催化活性较高，以尿素为沉淀剂制备的催化剂给出1073K时的CH4和CO2转化率分别为8．1％和17．6％，高温反应不仅导致金晶粒的聚集，而且存在明显的金流失现象。     

Correlation of the Catalytic Activity for Oxidation Taking Place on Various TiO2 Surfaces with Surface OH Groups and Surface Oxygen Vacancies

Three catalytic oxidation reactions have been studied: The ultraviolet (UV) light induced photocatalytic decomposition of the synthetic dye sulforhodamine B (SRB) in the presence of TiO₂ nanostructures in water, together with two reactions employing Au/TiO₂ nanostructure catalysts, namely, CO oxidation in air and the decomposition of formaldehyde under visible light irradiation. Four kinds of TiO₂ nanotubes and nanorods with different phases and compositions were prepared for this study, and gold nanoparticle (Au‐NP) catalysts were supported on some of these TiO₂ nanostructures (to form Au/TiO₂ catalysts). FTIR emission spectroscopy (IES) measurements provided evidence that the order of the surface OH regeneration ability of the four types of TiO₂ nanostructures studied gave the same trend as the catalytic activities of the TiO₂ nanostructures or their respective Au/TiO₂ catalysts for the three oxidation reactions. Both IES and X‐ray photoelectron spectroscopy (XPS) proved that anatase TiO₂ had the strongest OH regeneration ability among the four types of TiO₂ phases or compositions. Based on these results, a model for the surface OH group generation, absorption, and activation of molecular oxygen has been proposed: The oxygen vacancies at the bridging O^2? sites on TiO₂ surfaces dissociatively absorb water molecules to form OH groups that facilitate adsorption and activation of O₂ molecules in nearby oxygen vacancies by lowering the absorption energy of molecular O₂. A new mechanism for the photocatalytic formaldehyde decomposition with the Au/TiO₂ catalysts is also proposed, based on the photocatalytic activity of the Au‐NPs under visible light. The Au‐NPs absorb the light owing to the surface plasmon resonance effect and mediate the electron transfers that the reaction needs.     

溶剂化金属原子浸渍法制备聚合物固载Co Ag催化剂Ⅰ.组成与结构表征

为避免有机聚合物因热稳定性差而不能用高温氢气还原金属制备聚合物负载催化剂的弱点,采用溶剂化金属原子浸渍法在温和的条件下直接把零价金属负载在聚合物上,制备了几种不同金属含量的ＣｏＡｇ催化剂,用Ｘ－ 射线衍射,Ｘ－ 射线光电子能谱和磁测定对催化剂进行表征并和普通浸渍法制得的相同金属含量的催化剂进行比较,表明溶剂化金属原子浸渍法制得催化剂的金属粒度小于普通浸渍法制得的催化剂,而且前者的零价金属含量也高于后者。溶剂化金属原子浸渍法制得的催化剂Ｃｏ 在表面上,而普通浸渍法制得催化剂Ｃｏ 在表面和体相的金属含量基本相同。     

Milling Down to Nanometers: A General Process for the Direct Dry Synthesis of Supported Metal Catalysts

Supported catalysts are among the most important classes of catalysts. They are typically prepared by wet‐chemical methods, such as impregnation or co‐precipitation. Here we disclose that dry ball milling of macroscopic metal powder in the presence of a support oxide leads in many cases to supported catalysts with particles in the nanometer size range. Various supports, including TiO₂, Al₂O₃, Fe₂O₃, and Co₃O₄, and different metals, such as Au, Pt, Ag, Cu, and Ni, were studied, and for each of the supports and the metals, highly dispersed nanoparticles on supports could be prepared. The supported catalysts were tested in CO oxidation, where they showed activities in the same range as conventionally prepared catalysts. The method thus provides a simple and cost‐effective alternative to the conventionally used impregnation methods.     

Nanosized Au/C catalyst obtained from a tetraamminegold(III) precursor: Synthesis,characterization, and catalytic activity in low-temperature CO oxidation

A method in which the water-soluble complex [Au(NH₃)₄](NO₃)₃ is used as the active-component precursor is suggested for preparing nanosized Au/C catalysts (C = Sibunit, a mesoporous carbon material). The complex is unreadily reducible by the carbon matrix and can be involved in cation exchange with proton-containing groups of the support. This method is referred to as cationic adsorption. It has been demonstrated by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy that the catalyst prepared in this way and treated with H₂ at 400°C contains size-uniform gold metal particles with a dominant diameter of <5 nm. The greater part of the gold particles is located on the outer surface of the Sibunit granules; that is, an egg shell type distribution of the active component takes place. The catalyst containing 1.3 wt % Au shows high activity in CO oxidation with excess humid air at 40°C. In this respect, it is far superior to the Au/C catalysts prepared by conventional methods (deposition-precipitation and impregnation), in which the typical gold particle size is several tens of nanometers.     

Carbon Monoxide Oxidation by Polyoxometalate‐Supported Gold Nanoparticulate Catalysts: Activity,Stability, and Temperature‐ Dependent Activation Properties

Nanoparticulate gold supported on a Keggin‐type polyoxometalate (POM), Cs₄[α‐SiW₁₂O₄₀]⋅n H₂O, was prepared by the sol immobilization method. The size of the gold nanoparticles (NPs) was approximately 2 nm, which was almost the same as the size of the gold colloid precursor. Deposition of gold NPs smaller than 2 nm onto POM (Au/POM) was essential for a high catalytic activity for CO oxidation. The temperature for 50 % CO conversion was −67 °C. The catalyst showed extremely high stability for at least one month at 0 °C with full conversion. The catalytic activity and the reaction mechanism drastically changed at temperatures higher than 40 °C, showing a unique behavior called a U‐shaped curve. It was revealed by IR measurement that Au^δ+ was a CO adsorption site and that adsorbed water promoted CO oxidation for the Au/POM catalyst. This is the first report on CO oxidation utilizing Au/POMs catalysts, and there is a potential for expansion to various gas‐phase reactions.     

Carbon Monoxide Oxidation by Polyoxometalate‐Supported Gold Nanoparticulate Catalysts: Activity,Stability, and Temperature‐ Dependent Activation Properties

Nanoparticulate gold supported on a Keggin‐type polyoxometalate (POM), Cs₄[α‐SiW₁₂O₄₀]?n H₂O, was prepared by the sol immobilization method. The size of the gold nanoparticles (NPs) was approximately 2 nm, which was almost the same as the size of the gold colloid precursor. Deposition of gold NPs smaller than 2 nm onto POM (Au/POM) was essential for a high catalytic activity for CO oxidation. The temperature for 50 % CO conversion was ?67 °C. The catalyst showed extremely high stability for at least one month at 0 °C with full conversion. The catalytic activity and the reaction mechanism drastically changed at temperatures higher than 40 °C, showing a unique behavior called a U‐shaped curve. It was revealed by IR measurement that Au^δ+ was a CO adsorption site and that adsorbed water promoted CO oxidation for the Au/POM catalyst. This is the first report on CO oxidation utilizing Au/POMs catalysts, and there is a potential for expansion to various gas‐phase reactions.