Promotional effect of spilt-over hydrogen on m-xylene isomerization over NiS/Al2O3-USY

Gaseous hydrogen promoted markedly the catalytic activity of ultrastable Y zeolite (USY) for m-xylene isomerization under the conditions of 603 K and 1.0 MPa, when it was physically mixed with sulfided nickel supported on Al2O3 (NiS/Al2O3), whereas in the present system the NiS/Al2O3 component only did not show any effective activity for the reaction or effects of suppressing the coke formation on the USY zeolite. The H-D exchange rate of the OH groups on the USY zeolite surface in the NiS/Al2O3 -USY hybrid catalyst is five times higher than that of USY alone. It is strongly suggested that active hydrogen species formed on NiS sites and spilled over to Al2O3 and then to USY promote the acid catalysis on the USY.