Effect of Pt and H-2 on n-butane isomerization over Fe and Mn promoted sulfated zirconia

The activity of a 0.4 wt% Pt-containing Fe and Mn promoted sulfated zirconia (PtSFMZ) catalyst in n-butane isomerization at 35 degrees C was compared to that of a Pt-free catalyst (SFMZ). The maximum rate of n-butane conversion observed in helium over PtSFMZ was found to be 2.5 times higher than that over the SFMZ catalyst under the same conditions. It is believed that n-butane isomerization proceeds via a bimolecular mechanism in which the formation of hydrogen-deficient intermediates (carbenium ions and butenes) is necessary and the presence of transition metals such as Pt, Fe, and Mn on sulfated zirconia facilitates the formation/accumulation of these intermediates and increases their stability on the catalyst surface. The presence of H-2 had a strong negative effect on n-butane conversion over PtSFMZ, but had no effect over SFMZ. The negative effect of H-2 On PtSFMZ catalyst in n-butane isomerization reaction was attributed to the decreased concentration of butenes in the presence of hydrogen atoms which are formed by the dissociation of H-2 on Pt. The ability of calcined Pt-containing catalysts to activate hydrogen at 35 degrees C was demonstrated. Reduced SFMZ with or without Pt was not active at 35 degrees C regardless of the nature of the carrier gas. (C) 1996 Academic Press, Inc.