CATALYTIC HYDRODESULPHURIZATION OF THIOPHENE: V. THE HYDROTHIOPHENES. SELECTIVE POISONING AND ACIDITY OF THE CATALYST SURFACE

Abstract

The hydrogenolysis of tetrahydrothiophene over sulphided cobalt molybdate – alumina was shown to proceed in two ways. The main reaction was hydrodecyclization to n-butanethiol and conversion of the latter to butenes and butane; the second and less prominent reaction involved dehydrogenation to thiophene, which was also desulphurized. The overall desulphurization activity decreased in the order n-butanethiol > tetrahydrothiophene > 2,3-dihydrothiophene > thiophene. A better understanding of the dual catalytic nature of the catalyst resulted from selective poisoning experiments with H₂S, thiophene, methylthiophene, pyridine, and NH₃. The sites responsible for olefin hydrogenation were shown to have strong affinity for thiophenes, H₂S, and pyridine, as well as limited capacity to dehydrogenate thiolane and desulphurize thiophenes. Sites weakly electrophilic in character were also shown to be present on the catalyst surface. These could be poisoned only by ammonia or alkali and have been identified with the bulk of the desulphurization in the hydrogenolysis of thiophenes, hydrothiophenes, and thiol.