M-Xylene transformation over Ni/SAl 2O 3-USY hybrid catalysts Effects of hydrogen spillover

Abstract

m-Xylene transformation (isomerization and aromatics hydrogenation) on Y zeolite (USY) was markedly promoted by the physically mixed sulfided nickel supported on Al 2O 3 (Ni/SAl 2O 3) in the presence of hydrogen, while Ni/SAl 2O 3 showed no activity for these reactions, and coke deposition on USY and m-xylene disproportionation were not affected by Ni/SAl 2O 3. Also, under nitrogen atmosphere, all reactions were unaffected by Ni/SAl 2O 3. Studies of H-D exchange of OH groups on USY zeolite with gaseous D 2 by FT-IR spectroscopy showed that the ratio of the exchange rate of USY, Al 2O 3-USY and Ni/SAl 2O 3-USY catalyst was 3.8, 1 and 14.5, respectively, at 523 K and 62.5 kPa D 2. It was concluded that the H-D exchange of OH groups (including Brönsted acid sites) on USY surface in the Ni/SAl 2O 3-USY catalyst was mainly due to hydrogen spillover through NiS site dissociating gaseous hydrogen, with the spillover hydrogen migrating to the USY surface. This probably promoted m-xylene isomerization and helped maintain a higher activity of hydrogenation for aromatic rings on the zeolite.