Nonuniformly active $Pt/SiO_2$ catalyst

Abstract

Seven different nonuniformly-active Pt/$SiO_2$ catalysts were prepared in the ion exchange method with the variation of contact time during the ion exchange process to investigate the effect of contact time upon the content and distribution of platinum in the catalyst. Pt uptake of the silica support was measured with an atomic absorption spectrophotometer and compared with the results of the transient diffusion equation solved by the finite difference method under some appropriate assumptions. Deposited Pt profile in the silica particle was also predicted from the theoretical analysis. Surface structure of the catalysts was investigated by use of the gas chromatographic pulse technique of hydrogen chemisorption measurement. All the catalysts prepared were found to have H/Pt ratio of approximately unity, therefore surface of highly-dispersed state. Catalytic reaction rates on these nonuniformly-active catalysts were explained theoretically with the concepts of effectiveness factor and apparent effectiveness factor, and were actually measured using the vapor phase hydrogenation of cyclohexene as a test reaction. Experimental results showed good agreement with the predictions from the theoretical analysis