Showing papers by "Masatake Haruta published in 2004"

Gold as a novel catalyst in the 21st century: Preparation, working mechanism and applications

Abstract: Gold can be deposited as nanoparticles on a variety of support materials by coprecipitation or deposition-precipitation of Au(OH)3, grafting of organo-gold complexes such as dimethyl-Au(III)-acetylacetonate, mixing of colloidal Au particles, and vacuum deposition. Owing to the moderate adsorption of at least one of reactants (for example, CO) on the edges and corners of Au nanoparticles and to the activation of the counter reactant (for example, O2) at the perimeter interface with the supports, supported Au nanoparticle catalysts exhibit unique and practically useful catalytic properties at relatively low temperature below 473K. They have already been commercially used for deodorizers in rest rooms in Japan and will find growing applications in indoor air quality control, pollutant emission control, production of hydrogen energy carrier, and innovations in chemical processes. Cluster science of Au may also open an exciting area of research showing some magic numbers for dramatic changes in reactivity.

Catalysis by Gold Nanoparticles: Epoxidation of Propene

Abstract: Supported nano-gold catalysts have attracted rapidly growing interest due to their potential applicability to various reactions of industrial and environmental significance. In this article, we focus on the advances related to the direct vapor-phase oxidation of propene to propene oxide in the presence of molecular oxygen and hydrogen over gold catalysts supported on Ti-incorporated silica materials prepared by different methods. The importance of catalyst preparation and pretreatment method, nature of support material, Au particle size and loading amount is emphasized. Possibilities to enhance the catalyst performance by using promoters and by silylation are also discussed.

Nanoparticulate Gold Catalysts for Low-Temperature CO Oxidation

Abstract: Gold can be deposited as nanoparticles on a variety of support materials by coprecipitation, deposition-precipitation of Au(OH)3 , grafting of organo-gold complexes such as dimethyl-Au(III)-acetylacetonate, mixing of colloidal Au particles, and vacuum deposition The unique and practically useful catalytic performance of Au emerges by the strong contact with the support, the selection of support materials, and the size control of Au particles The oxidation of CO can take place even at a temperature as low as 200 K, owing to the moderate adsorption of CO on the edges and corners of Au nanoparticles and to the activation of O2 , probably at the perimeter interface with the supports However, an exception is that acidic supports such as Al2O3-SiO2 and activated carbon do not lead to low temperature CO oxidation, which imposes an essential scientific question related to polymer electrolyte fuel cells A comprehensive mechanism for low-temperature CO oxidation is presented that can account for the whole catalytic behavior of supported gold catalysts : an increase in TOF with a decrease in the diameter of Au particles, large difference in the enhancing effect of moisture among support metal oxides, zeroth order kinetics at concentrations of CO and O2 above 01 vol%, and low apparent activation energies

Effect of Impurity and Pretreatment Conditions on the Catalytic Activity of Au Powder for CO Oxidation

Abstract: Recent X-ray photoelectron spectrometer(XPS) analysis of Au powder synthesized by evaporating high purity gold metal (> 99. 99%) in an inert gas detected impurity metals such as Ag and In at levels which far exceed those expected from the impurity levels of raw gold metal. Several samples of Au powder containing different amount of impurity metals were prepared to examine whether the activity of the Au powder for CO oxidation depends upon the impurity or not. The activity of the powder showed a strong correlation with the surface concentration of Ag.

Gold as a Novel Catalyst in the 21st Century: Preparation, Working Mechanism and Applications

Abstract: Gold can be deposited as nanoparticles on a variety of support materials by coprecipitation or deposition-precipitation of Au(OH)3, grafting of organo-gold complexes such as dimethyl-Au(III)-acetylacetonate, mixing of colloidal Au particles, and vacuum deposition. Owing to the moderate adsorption of at least one of reactants (for example, CO) on the edges and corners of Au nanoparticles and to the activation of the counter reactant (for example, O2) at the perimeter interface with the supports, supported Au nanoparticle catalysts exhibit unique and practically useful catalytic properties at relatively low temperature below 473K. They have already been commercially used for deodorizers in rest rooms in Japan and will find growing applications in indoor air quality control, pollutant emission control, production of hydrogen energy carrier, and innovations in chemical processes. Cluster science of Au may also open an exciting area of research showing some magic numbers for dramatic changes in reactivity.

Vapor-phase epoxidation of propylene using H2/O2 mixture over gold catalysts supported on non-porous and mesoporous titania-silica: effect of preparation conditions and pretreatments prior to reaction

Abstract: Ti-doped nonporous silica was used as a support to prepare nanometer gold catalysts by the deposition–precipitation method for the direct vapor-phase epoxidation of propylene with O2 and H2. Both the catalysts dried under vacuum at room temperature and the catalysts calcined at 573 K in air exhibited catalytic activity to form PO even at a temperature as low as 323 K. The calcined catalysts were more stable and more active at higher temperatures than the dried catalysts. Simple filtration after aging the suspension resulted in the catalysts more active and selective but less stable than the complete washing of the solid precursors. Pretreatment in argon appreciably increased the catalytic activity and H2 efficiency over the Au catalysts deposited on Ti-doped nonporous silica, which was opposite to the case of Au/Ti-MCM catalysts. Similar deactivation rate of Au catalysts supported on a variety of titania–silica supports with different porosities suggests that quick deactivation of Au catalysts within hours is mainly affected by the surface properties rather than the pore structure and diffusion limitation of the supports.

Optical and electrical H/sub 2/- and NO/sub 2/-sensing properties of Au/In/sub x/O/sub y/N/sub z/ films

Abstract: In this paper, we describe the optical and electrical gas-sensing properties of In/sub x/O/sub y/N/sub z/ films with an ultrathin gold promoter overlayer. We have fabricated In/sub x/O/sub y/N/sub z/ films with a nanocrystalline porous structure by RF-sputtering in Ar/N/sub 2/ followed by an annealing process. Gold particles with 20-30-nm diameter have been formed on top of the In/sub x/O/sub y/N/sub z/ films by dc sputtering and an annealing process. We have investigated the optical H/sub 2/and NO/sub 2/-sensing properties (change of absorbance) and also the electrical sensing effect (change of electrical resistance) for these two gases. A combined optical/electrical sensor for H/sub 2//NO/sub 2/ is proposed.

Optical and Electrical H - and NO -Sensing Properties of Au In O N Films

Abstract: In this paper, we describe the optical and electrical gas-sensing properties of In O N films with an ultrathin gold promoter overlayer. We have fabricated In O N films with a nanocrystalline porous structure by RF-sputtering in Ar N followed by an annealing process. Gold particles with 20-30-nm diameter have been formed on top of the In O N films by dc sputtering and an annealing process. We have investigated the optical H - and NO -sensing properties (change of absorbance) and also the electrical sensing effect (change of electrical resis- tance) for these two gases. A combined optical/electrical sensor for H NO is proposed. Index Terms—Au In O N films, electrical NO sensor, optical H sensor.

Improved Long-range Order of Silicious MCM-41 by Gradual Heating of Synthesis Gel

Abstract: Mesoporous MCM-41 with fiber-like morphology and a high degree of long-range internal order in micrometer range, could be prepared by very gradual heating of the precursor gel to the crystallization temperature.