Metal/zirconia catalysts for the synthesis of methanol: characterization by vibrational spectroscopy |
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Authors: | A. Wokaun J. Weigel M. Kilo A. Baiker |
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Affiliation: | (1) Physical Chemistry II, University of Bayreuth, D-95440 Bayreuth, Germany;(2) Department of Chemical Engineering and Industrial Chemistry, ETH Zentrum, CH-8092 Zürich, Switzerland |
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Abstract: | The activation of carbon dioxide by catalytic hydrogenation has been studied as a route for methanol synthesis. Metal/zirconia catalysts suitable for this reaction have been prepared by (i) activation of amorphous metal alloys [1] or (ii) coprecipitation of amorphous zirconia and metal oxides [2]. Vibrational spectroscopy has been used to obtain information on the catalytic reaction mechanism, by the in situ identification of adsorbed species and intermediates under reaction conditions.The reverse water-gas shift reaction, producing CO from CO2 and hydrogen, plays a crucial role in the reaction mechanism. This reduction is shown to proceed via surface formate, adsorbed close to the metal/zirconia interface. Over Pd/ZrO2 and Ni/ZrO2, formate is reduced to methane without further observable intermediates. Pivotal intermediates on the route to methanol, as observed on Cu/ZrO2 catalysts, are -bound formaldehyde and surface methylate. Addition of silver as a promoter can result in enhanced selectivities and productivities for methanol formation. The synergy between the two metals becomes evident from the spectroscopic measurements; the most prominent feature of the silver-promoted catalysts is a high concentration of surface formaldehyde, which is either preferentially formed or stabilized by the silver component. |
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