Pt/SO42−-ZrO2 catalysts prepared from Pt organometallic compounds

Abstract

New Pt/SO42−-ZrO2 catalysts were prepared using precalcined SO42−-ZrO2 and organometallic Pt precursors. The objective was to obtain a bifunctional catalyst with improved metal properties, which are mostly suppressed in Pt/SO42−-ZrO2 prepared in a standard fashion. The synthesis route used low temperatures to form the Pt particles in order to avoid sulfate decomposition and Pt poisoning. The use of precalcined zirconia decreased ionic diffusion, related to crystallization of the gel and encapsulation of Pt particles. As detected by TPR and cyclohexane dehydrogenation tests, after reducing at 270 °C, Pt on the new catalyst had metallic properties. Its dehydrogenation activity was higher than that of a standard Pt/SO42−-ZrO2 catalyst (prepared from H2PtCl6). After activating in air at 300 °C, its activity for n-butane isomerization (300 °C, 1 atm., H2:n-C4=6, WHSV=1 h−1) was low, very likely because of incomplete elimination of adsorbed water. After activation in air at 600 °C, the isomerization activity was almost similar to that of standard Pt/SO42−-ZrO2 but the dehydrogenation activity decreased to negligible values. The deleterious interaction between Pt and SO42−-ZrO2 that occurred during calcination was possibly related to oxidation of the metal. On the other side, high reduction temperatures did not enhance the metal activity beyond the level obtained after reducing at 270 °C. On the contrary, the higher the reduction temperature, the lower the activity for cyclohexane dehydrogenation that was obtained. This effect was seemingly related to poisoning by sulfur compounds. The new materials could be potentially useful for reacting systems needing a bifunctional catalyst and an acid function like SO42−-ZrO2 but their operation is limited if high temperatures in air or H2 are necessary for activation.