Study on Au/Al2O3 catalysts for low-temperature CO oxidation in situ FT-IR

Au/Al2O3 catalyst was prepared by a modified anion impregnation method and investigated with respect to its initial activity and stability for low-temperature CO oxidation. The activity changes of the catalyst were examined after separate treatment in CO+O2 or CO2+O2. Furthermore, in situ FT-IR studies were performed to investigate the species on the surface when CO or CO+O2 or CO2+O2 was selected separately as adsorption gas. The results showed that Au/Al2O3 catalyst exhibited very high initial activity, but the catalytic activity was found to decrease gradually during CO oxidation with time on stream. And also, the activity of the catalyst declined after treatment in CO+O2 or CO2+O2. The formation and accumulation of carbonate-like species during CO oxidation or treatment in CO+O2 or CO2+O2 might be mainly responsible for the activity decrease, which was reversible.     

Increasing the number of oxygen vacancies on TiO2 by doping with iron increases the activity of supported gold for CO oxidation

The addition of iron to high-area TiO2 (Degussa P25, a mixture of anatase and rutile) increases the number of oxygen defect sites that react with O2 to form peroxide and superoxide species. In the presence of gold nanoclusters on the TiO2 surface, the superoxide species become highly reactive, and the activity of the supported gold catalyst for CO oxidation is approximately twice that of the most active comparable catalysts described in the literature. Images of the catalyst obtained by scanning transmission electron microscopy combined with spectra of the catalyst measured in the working state (Raman, extended X-ray absorption fine structure, and X-ray absorption near-edge structure) indicate strong interactions of gold with the support and the presence of iron near the interfaces between the gold clusters and the TiO2 support. The high activity of the catalysts is attributed to the presence of defects in these sites that activate oxygen.     

Geometrical Structure of the Gold–Iron(III) Oxide Interfacial Perimeter for CO Oxidation

The geometrical structure of the Au‐Fe₂O₃ interfacial perimeter, which is generally considered as the active sites for low‐temperature oxidation of CO, was examined. It was found that the activity of the Au/Fe₂O₃ catalysts not only depends on the number of the gold atoms at the interfacial perimeter but also strongly depends on the geometrical structure of these gold atoms, which is determined by the size of the gold particle. Aberration‐corrected scanning transmission electron microscopy images unambiguously suggested that the gold particles, transformed from a two‐dimensional flat shape to a well‐faceted truncated octahedron when the size slightly enlarged from 2.2 to 3.5 nm. Such a size‐induced shape evolution altered the chemical bonding environments of the gold atoms at the interfacial perimeters and consequently their catalytic activity. For Au particles with a mean size of 2.2 nm, the interfacial perimeter gold atoms possessed a higher degree of unsaturated coordination environment while for Au particles with a mean size of 3.5 nm the perimeter gold atoms mainly followed the atomic arrangements of Au {111} and {100} facets. Kinetic study, with respect to the reaction rate and the turnover frequency on the interfacial perimeter gold atom, found that the low‐coordinated perimeter gold atoms were intrinsically more active for CO oxidation. ¹⁸O isotopic titration and Infrared spectroscopy experiments verified that CO oxidation at room temperature occurred at the Au‐Fe₂O₃ interfacial perimeter, involving the participation of the lattice oxygen of Fe₂O₃ for activating O₂ and the gold atoms for CO adsorption and activation.     

Catalytic oxidation of carbon monoxide over Au/Fe2O3 preparations

Low temperature catalytic oxidation of carbon monoxide has been studied over Au/Fe₂O₃. On the coprecipitated samples the catalytic activity shows a maximum at a gold content of about 5%. Calcination of Au/Fe₂O₃ decreases the catalytic activity and the stability. The catalytic activity measured is the highest ever reported in the literature on Au/Fe₂O₃ preparations.     

CO oxidation mechanism on CeO(2)-supported Au nanoparticles

Density functional theory was used to study the CO oxidation catalytic activity of CeO(2)-supported Au nanoparticles (NPs). Experimental observations on CeO(2) show that the surface of CeO(2) is enriched with oxygen vacancies. We compare CO oxidation by a Au(13) NP supported on stoichiometric CeO(2) (Au(13)@CeO(2)-STO) and partially reduced CeO(2) with three vacancies (Au(13)@CeO(2)-3VAC). The structure of the Au(13) NP was chosen to minimize structural rearrangement during CO oxidation. We suggest three CO oxidation mechanisms by Au(13)@CeO(2): CO oxidation by coadsorbed O(2), CO oxidation by a lattice oxygen in CeO(2), and CO oxidation by O(2) bound to a Au-Ce(3+) anchoring site. Oxygen vacancies are shown to open a new CO oxidation pathway by O(2) bound to a Au-Ce(3+) anchoring site. Our results provide a design strategy for CO oxidation on supported Au catalysts. We suggest lowering the vacancy formation energy of the supporting oxide, and using an easily reducible oxide to increase the concentration of reduced metal ions, which act as anchoring sites for O(2) molecules.     

Oxidation chemistry of poly(ethylene glycol)-supported carbonylruthenium(II) and dioxoruthenium(VI) meso-tetrakis(pentafluorophenyl)porphyrin

[Ru(II)(F(20)-tpp)(CO)] (1, F(20)-tpp=meso-tetrakis(pentafluorophenyl)porphyrinato dianion) was covalently attached to poly(ethylene glycol) (PEG) through the reaction of 1 with PEG and sodium hydride in DMF. The water-soluble PEG-supported ruthenium porphyrin (PEG-1) is an efficient catalyst for 2,6-Cl(2)pyNO oxidation and PhI==NTs aziridination/amidation of hydrocarbons, and intramolecular amidation of sulfamate esters with PhI(OAc)(2). Oxidation of PEG-1 by m-CPBA in CH(2)Cl(2), dioxane, or water afforded a water-soluble PEG-supported dioxoruthenium(VI) porphyrin (PEG-2), which could react with hydrocarbons to give oxidation products in up to 80 % yield. The behavior of the two PEG-supported ruthenium porphyrin complexes in water was probed by NMR spectroscopy and dynamic light-scattering measurements. PEG-2 is remarkably stable to water. The second-order rate constants (k(2)) for the oxidation of styrene and ethylbenzene by PEG-2 in dioxane-water increase with water content, and the k(2) values at a water content of 70 % or 80 % are up to 188 times that obtained in ClCH(2)CH(2)Cl.     

常温常湿条件下Au/MeO~x催化剂上CO氧化性能

利用共沉淀法制备了Au/MeO~x催化剂(Me=Al,Co,Cr,Cu,Fe,Mn,Ni,Zn)。在常温常湿条件下,考察了不同氧化物负载的金基催化剂的CO氧化性能。结果表明,氧化物种类对催化剂的活性和稳定性均有较大的影响。Cu,Mn,Cr等氧化物负载的金基催化剂的活性较差,而Zn,Fe,Co,Ni,Al等金属氧化物负载的金基催化剂可将CO完全氧化,又具有一定的稳定性,在相同反应条件下,CO完全转化时的稳定性顺序为Au/ZnO>Au/α-Fe~2O~3>Au/Co~3O~4>Au/γ-Al~2O~3≈Au/NiO。还发现水对Au/MnO~x催化剂的活性和稳定性有负作用,而对180℃焙烧制备的Au/ZnO-180催化剂的活性和稳定性均有明显的湿度增强作用。     

Optimization of preparation conditions of Fe-Co nanoparticles in low-temperature CO oxidation reaction by taguchi design method

Mixed iron-cobalt oxide(Co/Fe molar ratio=1/5) are prepared using a simple co-precipitation procedure and studied for the catalytic oxidation of carbon monoxide.In particular,the effects of a range of preparation variables such as pH value when precipitation,aging temperature,precipitation agent type and aging time are investigated on the catalytic performance of synthesized Fe-Co oxides in CO oxidation reaction.In addition,the preparation factors were optimized by Taguchi design method.The optimized sample was characterized by XRD,N2 adsorption/desorption,TEM and TGA/DTA techniques.The results reveal that the optimized sample shows a mesoporous structure with a narrow pore size distribution centered in the range of 2-7nm.The sample prepared under optimized conditions has high activity and stability toward removal of carbon monoxide at lower temperatures.It is shown that different preparation variables influence the catalytic performance of Fe-Co oxide in CO oxidation reaction.     

Fabrication of Hierarchical Fe3O4@SiO2@P(4VP‐DVB)@Au Nanostructures and Their Enhanced Catalytic Properties

Hierarchical Fe₃O₄@SiO₂@P(4VP‐DVB)@Au nanostructures were prepared in which the slightly cross‐linked, thin poly(4‐vinylpyridine‐co‐divinylbenzene) (P(4VP‐DVB)) shells were constructed onto Fe₃O₄@SiO₂ nanospheres, followed by in situ embedding of gold nanocrystals homogeneously into the P4VP chains. These slightly cross‐linked chains, easily swollen by the reactants, make the gold nanocrystals accessible to the reactants, and the thin shell (about 15 nm) reduces the diffusion distance of the reactants to the active gold nanocrystals (about 5 nm), thereby enhancing their catalytic activity and utility. At the same time, confinement of gold nanocrystals within the P4VP shells prevents their migration and coagulation during catalytic transformations. Hence the nanocomposites exhibit high activity (up to 4369.5 h^?1 of turnover frequency (TOF)) and controllable magnetic recyclability without any significant loss of gold species after ten runs of catalysis in the reduction of 4‐nitrophenol.     

Characteristics of Active Site Formation in Co-Containing Catalysts for CO Oxidation on Chemically Different Supports

We have studied the catalytic activity in CO oxidation for cobalt-containing (1.2 mass % Co) catalysts on different supports: ZSM-5, Al₂O₃, SiO₂, and ERI. Using X-ray photoelectron spectroscopy (XPS), diffuse reflection electronic spectroscopy, and thermal programmed reduction we have established that the differences in the activity of Co-containing catalysts are due to different localization of the cobalt cations, the nature of their distribution in the surface layer of the catalyst, and the presence of cobalt ions Co_Oh in an environment of intralattice oxygen which have high reducibility.     

Synthesis of porous hematite nanorods loaded with CuO nanocrystals as catalysts for CO oxidation

Porous hematite (α-Fe2O3) nanorods with the diameter of 20-40 nm and the length of 80-300 nm were synthesized by a simple surfactant-assisted method in the presence of cetyltrimethylammonium bromide (CTAB).The α-Fe2O3 nanorods possess a mesostructure with a pore size distribution in the range of 5-12 nm and high surface area,exhibiting high catalytic activity for CO oxidation.CuO nanocrystals were loaded on the surface of porous α-Fe2O3 nanorods by a deposition-precipitation method,and the catalysts exhibited superior activity for catalytic oxidation of CO,as compared with commercial α-Fe2O3 powders supported CuO catalyst.The enhanced catalytic activity was attributed to the strong interaction between the CuO nanocrystals and the support of porous α-Fe2O3 nanorods.     

Catalytic performance and structural characterization of ferric oxide and its composite oxides supported gold catalysts for low-temperature CO oxidation

The preparation and catalytic activity of ferric oxide and its composite oxides supported gold catalysts for low-temperature CO oxidation were investigated detailedly, and characterized extensively by XRD, XPS, TPR, EC and XAFS techniques. It was found that containing highly dispersed Au of partially oxidized state, these nano-structured oxides supported Au/Fe2O3 and Au/NiFe2O4 catalysts had higher low-temperature activities. The possible catalytic active center is the gold of partially oxidized state (Auζ+).     

Promoting effect of tin oxide on the activity of silica- supported gold catalysts used in CO oxidation

In this study various Au/SnO_x-SiO₂ catalysts were prepared and tested in CO oxidation. It was found that the addition of tin oxide onto silica increased significantly the activity of Au/SiO₂ catalysts due to the alteration of the nanoenvironment of gold, which was evidenced by XPS and FTIR measurements.