ROLE OF SULFUR IN A SKEWED REFORMING CATALYST WITH A LOW PLATINUM CONTENT AND A HIGH RHENIUM-TO-PLATINUM RATIO

A skewed reforming catalyst (0.15% Pt and 0.35% Re) was successfully p resulfided by (NH4)2S solution. It was found that the optimum sulfur c ontent was about 0.01 wt.-%. A further addition of sulfur covered the surface platinum and caused a degradation of catalyst activity. The hy drogenolysis activity of n-hexane was suppressed and both isomerizatio n and aromatization selectivities were increased by presulfidation of the catalyst. It is interesting to note that the hydrogen uptake of th e catalyst at high temperatures is greatly enhanced by the addition of the correct amount of sulfur. Two major factors contributed to the hi gher stability of the catalyst after presulfidation, one was that sulf ur improved the hydrogen pool for the hydrogenation of the unsaturated carbonaceous overlayer to saturated alkanes at high temperatures, the other was that sulfur suppressed the adsorption of alkenes on the cat alyst, prevented the deep dehydrogenation of the carbonaceous overlaye r and impeded the reorganization of carbonaceous carbon into poisonous carbon.