Influence of nitrogen-containing components on the hydrodesulfurization of 4,6-dimethyldibenzothiophene over Pt, Pd, and Pt–Pd on alumina catalysts

Pyridine and piperidine inhibited the hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DM-DBT) over alumina-supported Pt, Pd, and Pt–Pd catalysts. The Pd catalyst was least sensitive and the Pt–Pd catalysts were most sensitive to the nitrogen-containing compounds. Pyridine was a stronger inhibitor than piperidine at low initial pressure, but the reverse was true at high initial pressure. Hydrogenation of the tetrahydro to the hexahydro and on to the perhydro sulfur-containing intermediate as well as the removal of sulfur from these intermediates was slowed down by piperidine and pyridine. The hydrogenation pathway in the hydrodesulfurization of 4,6-DM-DBT was inhibited much more than the direct desulfurization pathway. The hydrogenation of the desulfurized products 3,3′-dimethylcyclohexylbenzene and 3,3′-dimethylbiphenyl over the Pt–Pd catalysts was suppressed by piperidine and pyridine. Piperidine and pyridine substantially decrease the ability of noble metal particles to convert refractory molecules like 4,6-DM-DBT and diminish the advantage of bimetallic Pt–Pd over monometallic Pt or Pd catalysts.