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Structure sensitivity of selective co oxidation over precious metal catalysts

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2005
Atalık, Bora
In this study, the effect of Pt particle size on the reaction rate and selectivity of preferential oxidation of CO (PROX) reaction was investigated on Pt/Al2O3. 2% Pt/?-Al2O3 catalysts were prepared by incipient wetness method; the particle size of the catalysts was modified by calcination temperature and duration. Therefore, the relative amounts of low and high coordination atoms on the metal particle surface can be changed. Over these catalysts, first, the CO oxidation reaction was studied in the absence of hydrogen. The catalyst having the highest dispersion, i.e., lowest metal particle sizes, had the highest activity as indicated by its lowest light-off temperature. On the other hand, the turnover frequencies (TOF) of the catalysts were increasing with decreasing dispersion. The activation energy of the catalysts were also compared and examined: as the particle size increased, the activation energy decreased. In the second part, preferential oxidation of CO reaction in the presence of hydrogen was studied. Both CO conversion and selectivity first increased with increasing reaction temperature, then exhibited a maximum, and finally decreased. Both CO conversion and selectivity did not show any trend for different dispersed catalysts for ? (2PO2/PCO) was 1. In order to reach a definite conclusion about the structure sensitivity of selective CO oxidation, the experiments with different ?̕s and space times over the same catalysts should be performed.