Effects of silver loading and pretreatment with reaction gas on CO selective oxidation in H2 over silver catalyst

The removal of CO in H-2-rich gas by selective oxidation over Ag/SiO2 catalyst was investigated. The Ag loading and pretreatment with reaction gas at different temperatures had strong effects on the activity and selectivity of the catalyst for CO selective oxidation in H-2. The activiy of the catalyst increased with Ag loading, and the selectivity for CO oxidation decreased with reaction temperature. The temperature and the peak area of CO2 produced by CO-TPR were consistent with the reaction of CO selective oxidation in H-2. Moreover, the parabolic curves of the CO maximum conversion and its corresponding selectivity were obtained after the catalyst was treated with reaction gas at different temperatures. The highest CO conversion was obtained at 300 degreesC, and the selectivity at 200 degreesC. The surface structure of Ag particles may be changed during the process of treating the catalyst with H-2 at low temperature, which increased the activity and selectivity of the catalyst for CO oxidation. The facts that the larger Ag crystal particles were observed for the catalyst with higher Ag loading and the size of Ag particles decreased obviously after the sample was treated with reaction gas at high temperature (theta > 300 degreesC) indicated that the larger Ag particles under these conditions may favor CO selective oxidation at low temperature. Ag/SiO2 may be a promising catalyst for CO removal in the fuels for polymer-electrolyte type fuel cells at low temperature, and the activity and selectivity of the catalyst may be related with the size and the surface structure of Ag particles.