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Nanoporous Gold Catalysts for Selective Gas-Phase Oxidative Coupling of Methanol at Low Temperature

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Science  15 Jan 2010:
Vol. 327, Issue 5963, pp. 319-322
DOI: 10.1126/science.1183591

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Methanol Coupling Catalyzed with Gold

Gold surfaces can be effective catalysts for partial oxidation reactions, in part because lower interaction strengths of molecules absorbed on gold allow products to desorb before further unwanted oxidations occur. One challenge in these reactions is the low rate of formation of reactive atomic surface oxygen. Wittstock et al. (p. 319; see the Perspective by Christensen and Nørskov) created high–surface area gold catalysts by leaching silver from gold-silver alloys. This material proved to be an effective catalyst for partial oxidative coupling of methanol, yielding methyl formate. Residual silver appears to play a key role in activating the dissociation of molecular oxygen.

Abstract

Gold (Au) is an interesting catalytic material because of its ability to catalyze reactions, such as partial oxidations, with high selectivities at low temperatures; but limitations arise from the low O2 dissociation probability on Au. This problem can be overcome by using Au nanoparticles supported on suitable oxides which, however, are prone to sintering. Nanoporous Au, prepared by the dealloying of AuAg alloys, is a new catalyst with a stable structure that is active without any support. It catalyzes the selective oxidative coupling of methanol to methyl formate with selectivities above 97% and high turnover frequencies at temperatures below 80°C. Because the overall catalytic characteristics of nanoporous Au are in agreement with studies on Au single crystals, we deduced that the selective surface chemistry of Au is unaltered but that O2 can be readily activated with this material. Residual silver is shown to regulate the availability of reactive oxygen.

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