(A) study of SMSI in supported Pt catalysts by means of chemical reactions

Abstract

Catalytic activity of platinum supported on titania, γ-alumina, and silica was tested to study the SMSI in various reactions. In hydrogenation of cyclohexene, the activity of Pt/$TiO_2$ is decreased by reduction at high temperature. But oxidation followed by reduction restores the activity to the original level. This indicates the present of SMSI in Pt/$TiO_2$ . We can also find the same phenomena in silica-supported catalyst. But in dehydrogenation of cyclohexane reaction, these phenomena are found in only titania-supported catalyst and the temperature in which the SMSI can be induced shifts to higher temperature range. From the studies about SMSI and above experimental results, we suggest the mechanism that can be applied to our data. This mechanism involves two controlling steps, one of which is suppression of adsorption and the other is weakening effect of bond strength. This mechanism is based on reduction of supports. With this mechanism we can explain the SMSI as a general phenomenon in such a catalyst that can be reduced. Pt/γ-alumina catalyst was also tested to verify the redispersion phenomena. The hydrogenolysis of n-hexane on Pt/$TiO_2$ was carried out to investigate the effect of SMSI for isomerization and hydrogenolysis reactions. The yield of isomerization products showed the contrary results compared with hydrocracking products that showed the typical SMSI effects. These phenomena were interpreted by reduction of support.