The Effect of Sulfur on the Nonsteady State Reaction of Propane over a Platinum/Alumina Catalyst at 873 K

Abstract

The addition of sulphur to Pt/alumina catalysts, both in the preparation stage and in the gas phase during reaction, has been investigated as to the effect on catalyst activity and selectivity for propane dehydrogenation. The sole hydrocarbon product produced from pulses of propane over a freshly reduced Pt/alumina catalyst at 873 K in the absence of sulphur was methane, with concomitant carbon laydown. The effect on activity and selectivity of predosing the catalyst with hydrogen sulphide at 293 and 873 K was examined, as was the effect of cofeeding at ratios of 1:10 and 10:1 H2S:C3H8. Predosing at 873 K had the largest effect on selectivity, allowing the formation of propene from the first pulse of propane, whereas cofeeding required the build-up of sulphur on the surface before selectivity was achieved. Adding sulphur into the catalyst preparation was more effective than subsequent addition from the gas phase. The results also indicated that the selectivity observed was not directly related to the amount of sulphur on the surface. The presence of a hydrogen reservoir on the catalyst, which was available for reaction, was detected using catalysts reduced in deuterium. The results also indicated that hydrogen from adsorbed hydrogen sulphide could react with hydrocarbon fragments on the catalyst surface to produce methane.