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 presulfided by (NH4)2S solution. It was found that the optimum sulfur content was about 0.01 wt.-%. A further addition of sulfur covered the surface platinum and caused a degradation of catalyst activity. The hydrogenolysis activity of n-hexane was suppressed and both isomerization and aromatization selectivities were increased by presulfidation of the catalyst. It is interesting to note that the hydrogen uptake of the catalyst at high temperatures is greatly enhanced by the addition of the correct amount of sulfur. Two major factors contributed to the higher stability of the catalyst after presulfidation, one was that sulfur 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 catalyst, prevented the deep dehydrogenation of the carbonaceous overlayer and impeded the reorganization of carbonaceous carbon into poisonous carbon.