Neopentane Reactions over Bimetallic Pt-Sn/AI203 and Pt-Au/SiO2 Catalysts

The reaction of 2,2-dimethylpropane (neopentane) with hydrogen was studied over two series of supported bimetallic catalysts containing platinum as the primary group VIII metal and either gold or tin as the second metallic component. In both catalyst series the platinum nominal loading was maintained constant at 1 wt%. The loading of the second metal component was varied. An effort has been made to better understand the reactivity trends in these catalysts, by bringing the neopentane reactivity data into context with previously obtained n-hexane reaction results and extensive catalyst characterization data. Smail amounts of tin (1.0 Pt-0.1 Sn/AI203) caused the neopentane isomerization selectivity to drop in comparison to monometallic 1.0 Pt/AI203 . However, further addition of tin up to 1.0 wt% caused the neopentane isomerization selectivity to increase above that of the monometallic 1.0 Pt/A1203 sample. On adding excess tin (5.0 wt%) the activity of the catalyst became prohibitively low. Hence, there seemed to be an optimum loading of tin giving desirable selectivity characteristics at reasonable activity levels. The differences in isomerization selectivity in the case of the Pt-Au/SiO2 catalysts were not as significant as those observed for the Pt-Sn/A1203 catalysts. The trends in catalytic behavior were consistent with previously measured n-hexane reaction trends and could be interpreted on the basis of microstructural differences between the bimetallic catalysts. The effect of gold appeared to be mainly a geometric one, disrupting larger Pt ensembles. On the other hand, the role of tin appeared to go beyond a simple geometric effect. © 1991 Academic Press, Inc.