CO oxidation on Aun/TiO2 catalysts produced by size-selected cluster deposition

Planar model catalysts were prepared by deposition of size-selected gold clusters containing up to seven atoms on rutile TiO2 (110). Molecular oxygen is observed to bind inefficiently to the surface, probably at oxygen vacancies, and some oxygen also appears to bind to the gold clusters. Stable CO binding is observed atop gold for catalysts prepared by Au and Au2 deposition, but not for larger Aun. CO oxidation activity is strongly dependent on cluster size, with Au7-prepared samples >50 times more reactive than samples prepared by Au or Au2 deposition     

Influence of pretreatment conditions on low-temperature CO oxidation over Au/MOx/Al2O3 catalysts

Composite oxide MO_x/Al₂O₃ supported gold catalysts for low-temperature CO oxidation were prepared and investigated. The presence of transition metal oxide was proved to be beneficial to the improvement of catalytic performance of Au/Al₂O₃ catalysts for low-temperature CO oxidation. Furthermore, the influence of various pretreatment conditions on Au/MO_x/Al₂O₃ catalysts was studied carefully. The image of TEM showed that gold catalyst with small gold particles only in the form of a fine dispersion exhibited highly catalytic activity. The XPS, Fourier transform infrared (FTIR) spectroscopy characterization results of Au/FeO_x/Al₂O₃ catalyst showed that gold catalysts having partially oxidized gold species have the best catalytic performance. One possible pathway for CO oxidation on Au/FeO_x/Al₂O₃ catalyst is that the CO adsorbed on gold particles reacts with adsorbed oxygen, which is possible to occur on oxygen vacancies on the support or at the metal–support interface.     

Comparative studies of gold catalysts prepared via solvated metal atom impregnation and conventional impregnation: characterization and low-temperature co oxidation

Supported Au catalysts for low-temperature CO oxidation were prepared by solvated metal atom impregnation (SMAI) and conventional impregnation (CI). X-ray photoelectron spectroscopy investigations indicated that gold in all the samples was in the metallic state. TEM and XRD measurements showed that the mean diameter of Au particles prepared by SMAI was smaller than that of those prepared by CI with the same gold content. Catalytic tests showed that SMAI catalysts had higher CO oxidation activity than CI catalysts with the same compositions. Both SMAI and CI Au/TiO₂catalysts exhibited high activities in low temperature CO oxidation. Full CO conversion was obtained at 323 K for 3.1 wt.% Au/TiO₂ (SMAI) catalyst, which displayed higher activity than the 3.1 wt.% Au/D-72(SMAI) and 3.1 wt.% Au/TiO₂(CI). Although the sizes of gold particles prepared by the same method and supported on both TiO₂ and resin were comparable, the Au/TiO₂ catalysts showed significantly higher activities than the Au/resin catalysts with the same Au contents under the same reaction conditions. These results prove that not only the gold particle size, but also the support plays a key role in CO oxidation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Catalysis by supported gold: correlation between catalytic activity for CO oxidation and oxidation states of gold

X-ray absorption near-edge spectra and temperature-programmed oxidation and reduction data demonstrate that Au(I) and Au(0) are both present in working MgO-supported gold catalysts for CO oxidation. EXAFS data indicate gold clusters with essentially the same average diameter (about 30 A) in each catalyst sample. Thus, the results provide no evidence of an effect of gold cluster size on the catalytic activity, but both the catalytic activity and the surface concentration of Au(I) were found to decrease with increasing CO partial pressure (as Au(0) was increasingly formed), demonstrating that the catalytic sites incorporate Au(I).     

载体对负载型金催化剂上甲醛催化氧化的影响

采用沉积.沉淀法和氨水络合法制备了Al2O3,TiO2,CeO2和SiO2负载的纳米金催化剂,利用元素分析、x射线衍射、氮气物理吸附、程序升温还原、透射电镜和拉曼光谱等技术对催化剂进行了表征,并考察了其低温催化甲醛氧化活性.结果表明,Au/CeO2的催化性能最佳,在40℃时甲醛转化率仍能保持在80%以上.催化剂的活性同时受Au的化学状态和载体性质的影响.Au/CeO2催化剂较高的低温活性可能与离子态的Au物种有关,同时AuxCe1-xO2-δ固溶体的形成产生了大量的氧缺位,提高了氧的活化能力,也有助于提高催化剂的低温活性.     

Au/ZrLa掺杂 CeO2催化剂在CO氧化反应中优异的催化活性：锆镧协同作用

在过去的25年,纳米金催化剂上 CO氧化反应得到广泛研究,但始终没有一致的结论。这是因为影响纳米金催化活性的因素很多,包括金的价态、载体的性质、氧空位、金属与载体之间的相互作用等,尤其是各影响因素之间相互牵制,增加了催化反应机理的研究难度。氧化铈载体表面氧缺陷的浓度较高,有利于活性金属组分在其表面的稳定和分散,因此氧化铈纳米晶负载的 Au催化剂受到广泛关注。此外,当 CeO2晶格中部分 Ce被化学性质不同的其它元素取代后,可以促进 CeO2晶格氧的活化,提高氧的储放能力,从而有利于催化反应进行。因此,本文采用水热法合成了组成均匀的 CeO2, CeZrOx和 CeZrLaOx三个载体,并通过沉淀-沉积法负载金。利用 X射线衍射(XRD)、拉曼光谱(Raman)、X射线光电子能谱(XPS)、高分辨透射电镜(HRTEM)、X射线吸收精细结构(XAFS)和氢气程序升温还原(H2-TPR)等技术分析了催化剂的物相结构、表面性质、形貌以及金纳米颗粒的大小和价态等性质,并结合其在 CO氧化反应中催化性能的差异,探讨影响金催化剂活性的关键因素。 XRD, TEM, HRTEM和 XAFS结果表明,三个载体上所得金纳米颗粒的平均尺寸都在2–4 nm,且分散较好; XPS结果表明,影响催化剂活性的关键因素不是金的价态,而是载体表面的活性氧物种。从Raman结果可知,掺杂后的氧化铈载体上氧空位浓度明显增加,因而催化剂活性都有所提高。 H2-TPR进一步探讨了三个载体以及负载金后其氧化还原能力的变化,结果表明,金和载体之间的相互作用可以增强载体的氧化还原性能以及表面氧空位浓度,进一步提高了催化剂活性,而负载金催化剂氧化还原性能的变化与载体的组成密切相关。由于锆的掺杂可使金与载体之间相互作用减弱,而镧则增强了二者间相互作用,因此 Au/CeZrLaOx催化剂上锆和镧的协同掺杂作用使其表面活性氧物种浓度最高,低温时表现出最高的催化活性。     

金的化学状态对Au／CoCeOx催化剂CO氧化性能的影响

以CoCeOx复合氧化物为载体,采用沉积沉淀法制备了负载型的金催化剂,并通过不同温度的预处理控制Au的化学状态. 使用粉末X射线衍射、高分辨透射电子显微镜、程序升温还原和X射线光电子能谱对催化剂进行了表征,考察了在室温条件下该系列催化剂的一氧化碳氧化性能. 结果表明, Au/CoCeOx催化剂的CO氧化性能与催化剂表面Au 的含量成正比, Au 可能是反应的主要活性物种. 添加水汽对反应有一定的促进作用,但由于Au 不能稳定存在,特别是当催化剂表面Au 的含量过高时,在水汽的作用下Au 迅速发生歧化反应,使得催化剂的性能下降.     

Oxidation of Carbon Monoxide on Co-, Ni-, and Cu-containing Catalysts Prepared by Pyrolysis of Metal β-Diketonates on Synthetic Foamed Ceramics

Catalytic systems containing Co, Ni, and Cu composite coatings prepared by gas-phase thermolysis of metal acetylacetonates and hexafluoroacetylacetonates on synthetic foamed ceramics were suggested for oxidation of CO to CO₂. The relative activities of the catalysts and the kinetic and activation parameters of CO oxidation were determined. The catalytic activity depends on the catalyst preparation procedure.     

Insights into the oxidation and decomposition of CO on Au/alpha-Fe2O3 and on alpha-Fe2O3 by coupled TG-FTIR

CO oxidation and decomposition behaviors over nanosized 3% Au/alpha-Fe2O3 catalyst and over the alpha-Fe2O3 support were studied in situ via thermogravimetry coupled to on-line FTIR spectroscopy (TG-FTIR), which was used to obtain temperature-programmed reduction (TPR) curves and evolved gas analysis. The catalyst was prepared by a sonication-assisted Au colloid based method and had a Au particle size in the range of 2-5 nm. Carburization studies of H 2-prereduced samples were also made in CO gas. According to gravimetry, for the 3% Au/alpha-Fe2O3 catalyst, there were three distinct stages of CO interaction with the Au catalyst but only two stages for the catalyst support. At low temperatures (相似文献   

沉淀剂对AU/ZnO催化剂CO氧化性能及催化剂结构的影响

在25 C和进料中含水条件下,考察了由Na2CO3,(NH4)2CO3,NaOH和NH4OH等4种沉淀剂制备的Au/ZnO催化剂上CO氧化活性和稳定性.结果表明,沉淀剂影响Au/ZnO催化剂的前体组成、金粒子和ZnO粒子大小、比表面积及CO氧化性能.由NH4OH制备的Au/ZnO催化剂活性和稳定性较差,CO转化率只有15%;由其它3种沉淀剂制备的Au/ZnO催化剂的CO氧化活性和稳定性明显改善,可至少连续反应1 100 h,且保持CO完全氧化,其中Na2CO3是最佳沉淀剂.在反应过程中反应气氛可引起金粒子的聚集及在催化剂表面生成新的碱式碳酸锌物相.催化剂的稳定性与金粒子长大速度和碳酸根累积量有关.     

控制CO选择氧化反应中金催化剂热点形成的新方法

采用沉积-沉淀法制备了Al2O3和MOx-Al2O3(M=Fe,Zn)负载型金催化剂.室温下对其CO氧化及富氢条件下CO选择氧化催化活性进行了广泛的研究.催化剂床层温度由热电偶直接测定.催化剂表面温度与O2/CO的体积比以及CO和H2的浓度密切相关.在CO氧化反应过程中Au/Al2O3催化剂的温度可高达170°C,添加FeOx可使其降至55°C.利用一系列仪器(X射线衍射仪,X射线光电子能谱仪和透射电镜等)对催化剂的结构进行了表征.结果显示Al2O3负载型金催化剂热点的形成可以通过添加合适的助剂很好地控制.助剂的添加能够使催化剂活性中心由金属态Au变为AuIII,从而导致了CO选择氧化反应机理不同.     

Pt/MOx-SiO2 (M=Ce,Zr, Al)催化剂对CO和C3H8氧化性能的影响

采用共沉淀法制备质量比为1:1的MOx-SiO2(M=Ce,Zr,Al)复合氧化物,以此为载体采用浸渍法制备了铂基氧化型催化剂.考察了该系列催化剂在模拟柴油车尾气条件下,经SO2硫化前后对C3H8和CO的氧化性能.用X射线衍射(XRD)、低温N2吸附-脱附、氨气/氧气/二氧化碳程序升温脱附(NH3/O2/CO2-TPD)和X射线光电子能谱(XPS)等手段进行了表征.NH3-TPD证实催化剂表面存在多种酸中心,硫化后催化剂表面中强酸中心增多.O2-TPD证实催化剂表面存在α和β氧物种,硫化后催化剂表面氧脱附量减少.其中Pt/Al2O3-SiO2表面酸性最弱和表面氧脱附量最大.XPS结果表明新鲜催化剂经硫化后会使催化剂表面Pt的结合能降低.活性测试结果表明,三种催化剂对CO和C3H8的催化氧化活性均较好,其中Pt/ZrO2-SiO2抗SO2中毒性能最佳,具有良好的应用前景.     

Fundamental Aspects of Ceria Supported Au Catalysts Probed by In Situ/Operando Spectroscopy and TAP Reactor Studies

The discovery of the activity of dispersed gold nanoparticles three decades ago paved the way for a new era in catalysis. The unusual behavior of these catalysts sparked many questions about their working mechanism. In particular, Au/CeO₂ proved to be an efficient catalyst in several reactions such as CO oxidation, water gas shift, and CO₂ reduction. Here, by employing findings from operando X-ray absorption spectroscopy at the near and extended Au and Ce L_III energy edges, we focus on the fundamental aspects of highly active Au/CeO₂ catalysts, mainly in the CO oxidation for understanding their complex structure-reactivity relationship. These results were combined with findings from in situ diffuse reflectance FTIR and Raman spectroscopy, highlighting the changes of adlayer and ceria defects. For a comprehensive understanding, the spectroscopic findings will be supplemented by results of the dynamics of O₂ activation obtained from Temporal Analysis of Products (TAP). Merging these results illuminates the complex relationship among the oxidation state, size of the Au nanoparticles, the redox properties of CeO₂ support, and the dynamics of O₂ activation.     

Synthesis of gold and palladium nanoparticles supported on CuO/rGO using imidazolium ionic liquid for CO oxidation

A simple ionic liquid-assisted approach for the fabrication of graphene-based nanocomposite is reported. Pd–CuO/rGO and Au–CuO/rGO nanocomposites are successfully fabricated with the assistance of the ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate. The physicochemical features of nanocomposite are systematically characterized by XRD, FT-IR, Raman spectroscopy, XPS, TGA, FESEM, AFM, and HRTEM. Carbon monoxide has been used as a probe molecule to emphasize the performance of the fabricated materials. The results indicate that the incorporation of a little quantity of ionic liquid results in the creation of uniformly dispersed NPs simultaneously with the reduction of graphene oxide (GO) into rGO, which leads to a low-temperature CO oxidation process. Besides, the Au–CuO/rGO catalyst achieved excellent durability in CO oxidation for 14 h, without detectable deactivation. The low-temperature CO oxidation was mainly induced by the synergistic effects between the components of catalysts. The Au or Pd and CuO combination not only generates more interfaces, which is more favorable for the activation of oxygen but also enhances the catalyst reduction behavior. Consequently, a graphene composite catalyst can be considered a potential CO oxidation candidate.

     

Synthesis, characterization, and testing of supported Au catalysts prepared from atomically-tailored Au38(SC12H25)24 clusters

Nearly monodispersed Au(38)(SC(12)H(25))(24) clusters (1.7 ± 0.2 nm) were synthesized using a modified Brust process while utilizing a "thiol etching" approach for the ligand exchange. HRTEM, MALDI, FTIR, and XAS analysis confirmed the formation of the 38-atom clusters in solution. This solution was used to impregnate a microporous TiO(2) support to give 0.7% Au(38)/TiO(2) catalyst. Subsequent drying in air and treatment with H(2)/He at 400 °C removed most of the sulfur ligands, and also increased the Au cluster size to 3.9 ± 0.96 nm. XPS and EXAFS analysis of this supported catalyst showed trace levels of residual sulfides, apparently located at the Au-TiO(2) interface. CO oxidation tests on these supported clusters show an activation energy and range of TOFs comparable to those reported by others. These results suggest that supported Au clusters of controllable size can be prepared with this thiol-ligated solution-based method, providing a new approach to the synthesis of these catalysts.     

Nature of reactive O2 and slow CO2 evolution kinetics in CO oxidation by TiO2 supported Au cluster

Recent experiments on CO oxidation reaction using seven-atom Au clusters deposited on TiO2 surface correlate CO2 formation with oxygen associated with Au clusters. We perform first principles calculations using a seven-atom Au cluster supported on a reduced TiO2 surface to explore potential candidates for the form of reactive oxygen. These calculations suggest a thermodynamically favorable path for O2 diffusion along the surface Ti row, resulting in its dissociated state bound to Au cluster and TiO2 surface. CO can approach along the same path and react with the O2 so dissociated to form CO2. The origin of the slow kinetic evolution of products observed in experiments is also investigated and is attributed to the strong binding of CO2 simultaneously to the Au cluster and the surface.     

Ag－Ce／γ－Al_2O_3催化剂上CO的氧化

Ａｇ－Ｃｅ／γ－Ａｌ_２Ｏ_３催化剂上ＣＯ的氧化罗孟飞，袁贤鑫（杭州大学催化研究所，杭州３１００２８）关键词氧化银，氧化铈，氧化铝，负载型催化剂，一氧化碳，氧化银作为工业催化剂，常用于选择性氧化反应，如乙烯的环氧化＂＇，乙醇选择性氧化制乙醛［＇ｊ，甲苯...     

Mechanism of CO oxidation on catalysts prepared by pyrolysis of transition metal β-diketonates on a synthetic ceramic foam matrix

Kinetic and activation parameters of carbon monoxide oxidation on catalysts prepared by pyrolysis of the transition metals β-diketonates on synthetic ceramic foam matrices of different nature were measured in the absence of oxygen in the reaction mixture. Based on the kinetic data and infrared spectroscopy, the contributions of conjoint and split reaction mechanisms of CO oxidation as a function of temperature and nature of the carrier were estimated.     

Gold catalysts supported on ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for low-temperature CO oxidation

Gold catalysts with loadings ranging from 0.5 to 7.0 wt% on a ZnO/Al₂O₃ support were prepared by the deposition–precipitation method (Au/ZnO/Al₂O₃) with ammonium bicarbonate as the precipitation agent and were evaluated for performance in CO oxidation. These catalysts were characterized by inductively coupled plasma-atom emission spectrometry, temperature programmed reduction, and scanning transmission electron microscopy. The catalytic activity for CO oxidation was measured using a flow reactor under atmospheric pressure. Catalytic activity was found to be strongly dependent on the reduction property of oxygen adsorbed on the gold surface, which related to gold particle size. Higher catalytic activity was found when the gold particles had an average diameter of 3–5 nm; in this range, gold catalysts were more active than the Pt/ZnO/Al₂O₃ catalyst in CO oxidation. Au/ZnO/Al₂O₃ catalyst with small amount of ZnO is more active than Au/Al₂O₃ catalyst due to higher dispersion of gold particles.     

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.