Zn-promoted hydrogen exchange for methane and ethane on Zn/H-BEA zeolite: In situ H-1 MAS NMR kinetic study

Hydrogen (H/D) exchange between Bronsted acid sites of both the acidic form of zeolite beta (H-BEA) and Zn-loaded zeolite beta (Zn/H-BEA) and small alkanes (methane and ethane) has been studied by monitoring the kinetics of the exchange in situ with H-1 MAS NMR spectroscopy within the temperature range of 433-563 K. On Zn/H-BEA, the exchange has been found to be more than two orders of magnitude faster compared to that on H-BEA. The decrease of reaction temperature and activation energy of the exchange on Zn/H-BEA (86-88 kJ mol(-1)) compared to the acidic form of zeolite H-BEA (138 kJ mol(-1)) has been rationalized by the promoting effect of zinc. We propose that the mechanism of the H/D exchange on Zn/H-BEA involves Zn-alkyl species as intermediates. (c) 2007 Elsevier Inc. All rights reserved.