Chemisorption and disproportionation of carbon monoxide on palladium/silica catalysts of differing percentage metal exposed
- 1 January 1987
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 83 (9) , 2757-2764
- https://doi.org/10.1039/f19878302757
Abstract
Silica-supported palladium catalysts ranging from 5 to 80% metal exposed have been characterized by pulse adsorption/flow desorption of hydrogen and/or carbon monoxide. Measured gas uptakes were used to calculate an average CO to Pds ratio to determine whether CO chemisorption exhibits variation with metal particle size. Average values of CO/Pds range from 0.50 to 0.79, indicating a structure-sensitive adsorption. However, in view of experimental uncertainties only the lowest percentage exposed sample has a unique CO/Pds ratio of 0.5, indicative of bridge-bonded CO. All catalysts have adsorption stoichiometries less than unity. A structure-sensitive CO surface reaction occurs, in the vicinity of 575 K, during CO adsorption/desorption cycles between 300 and 725 K in the presence of either He or H2. Overall, the results suggest that CO dissociates into surface carbon either by disproportionation or by a hydrogen-assisted bond dissociation on the high-percentage exposed samples, but not on lower percentage exposed materials. A small amount of surface reconstruction may also occur.Keywords
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