Elsevier

Journal of Catalysis

Volume 178, Issue 2, 10 September 1998, Pages 566-575
Journal of Catalysis

Regular Article
Selective Vapor-Phase Epoxidation of Propylene over Au/TiO2Catalysts in the Presence of Oxygen and Hydrogen

https://doi.org/10.1006/jcat.1998.2157Get rights and content

Abstract

Gold has long been thought to be chemically inert, however, it has recently been proven that its catalytic performance is dramatically tunable by control of the particle size and by careful selection of the support metal oxide. A typical example is the selective oxidation of propylene in a gas containing oxygen and hydrogen. When gold is deposited on TiO2by a deposition–precipitation technique as hemispherical particles with diameters smaller than 4.0 nm it produces propylene oxide with selectivities higher than 90% and conversions of 1–2% at temperatures of 303–393 K. The oxidation of hydrogen to form water is depressed by propylene, whereas propylene oxidation is not only enhanced but also restricted to partial oxidation by hydrogen. The depression of hydrogen combustion by the presence of propylene and a new peak due to gold deposition in TPD spectra have indicated that propylene is adsorbed on the surfaces of both gold particles and the TiO2support. The reaction rate is almost independent on the concentration of propylene and increases linearly with increasing concentrations of O2and H2. The above results suggest that propylene adsorbed on a gold surface may react with oxygen species formed at the perimeter interface between the gold particles and the TiO2support through the reaction of oxygen with hydrogen. The effect of gold loading is surprising in that the reaction product switches from propylene oxide to propane when gold loading is decreased to 0.1 wt%. Careful TEM observation indicates that gold particles larger than 2.0 nm in diameter produce propylene oxide, whereas smaller gold particles produce propane.

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    J. J. BurtonR. L. Garten

    1

    Present address: Nippon Shokubai Co., Ltd., Nishi-Otabi 5-8, Suita, 564-0034 Japan.

    2

    To whom correspondence should be addressed. E-mail: haruta@onri. go.jp.

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