An investigation of the mechanism of the hydrodesulfurization of thiophene over sulfided CoMo Al₂O₃ catalysts. II. The effect of promotion by cobalt on the CS bond cleavage and double-bond hydrogenation/dehydrogenation activities of tetrahydrothiophene and related compounds

The CS bond cleavage reactions of tetrahydrothiophene and but-1-thiol with and without hydrogen, the dehydrogenation of tetrahydrothiophene, and the hydrogenation of but-l,3-diene and of but-1-ene at a temperature of 521 K have been examined at relatively low pressures and temperatures over three related Mo Al₂O₃ catalysts; one was unpromoted with Co and the others had different Co contents. The catalysts were activated prior to use by treatment in hydrogen sulfide at 573 K followed by hydrogen at 521 K. The products (but-1-ene, but-2-enes, butane, and but-l,3-diene) and product distributions from the reactions of tetrahydrothiophene were similar to those reported in Part I for the hydrosulfurization of thiophene; although but-1-thiol gave similar products, the product distribution was very different, there being much higher proportions of butane. There was no evidence under these conditions for interconversion of tetrahydrothiophene and but-1-thiol. It is concluded that ring hydrogenation of thiophene occurs prior to CS bond cleavage rather than vice versa; the hydrogenation and CS bond cleavage sites are distinct but interrelated and are both promoted by Co. These results and conclusions are compared and contrasted with those in the literature.