Iridium addition enhances hydrodesulfurization selectivity in 4,6-dimethyldibenzothiophene conversion on palladium

• Pd-Ir catalyst efficiently hydrodesulfurizes 4,6-dimethyldibenzothiophene.
• Ir addition to Pd improves HDS selectivity to 93% vs. 38% for mono Pd.
• Ir enhances direct desulfurization and CS hydrogenolysis in hydrogenation.
• Process pressure can be decreased from 5 to 3 MPa.

38% to 93% selectivity enhancement toward sulfur-free products was observed upon iridium addition to a palladium-only catalyst in the hydrodesulfurization of a refractory sulfur compound 4,6-dimethyldibenzothiophene (4,6-DMDBT) at the same 40% conversion from a 300 ppm, S-containing feed at 5 MPa and 300 °C. Pd promoted hydrogenation to sulfurous intermediates, while Ir catalyzed CS hydrogenolysis and also improved Pd resistance to sintering. The selectivity in the direct desulfurization path for the Ir-containing catalysts increased up to 26% versus 5% for the Pd-only catalyst. The bimetallic catalyst allowed for a decrease in S from 300 ppm to 11 ppm. It can be used at reduced pressure (3 MPa) with only a 15% decrease in hydrodesulfurization conversion as compared to the operation at 5 MPa.

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