Hydrogenation and deuterium exchange by spillover hydrogen of ethylbenzene adsorbed on H-USY zeolite

Abstract

Pt was synthesized within the pores of NaA zeolite and mixed with ethylbenzene (EB) chemisorbed on the acid sites in H-USY zeolite. The physical mixture was treated with D 2 at 75°C, and the temperature-programmed desorption products were analyzed by mass spectrometry. The reaction of EB with spillover hydrogen results in isotopic exchange, but not in saturation of the aromatic ring. For EB adsorbed on weaker acid sites, exchange occurs primarily with the aromatic hydrogens, whereas for EB chemisorbed on stronger acid sites there is, additionally, deuterium exchange with alkyl hydrogens. Isotopic exchange by spillover hydrogen is suggested to occur only for hydrogens on the carbocations. These results for catalysis imply that the increased activity for aromatic saturation observed for metals dispersed on acidic supports is not due to the generation of new catalytic sites on the support and reaction by spillover hydrogen.