IN-SITU H-1 MAS NMR-STUDIES OF THE H D EXCHANGE OF DEUTERATED PROPANEADSORBED ON ZEOLITE H-ZSM-5/

The hydrogen exchange in the propane-d(8) loaded zeolite H-ZSM-5 was m onitored by in situ H-1 MAS NMR spectroscopy within the temperature ra nge 457-543 K. Measurements of the H/D exchange between the acidic hyd roxyl groups of the zeolite and the adsorbed deuterated propane molecu les show that both methyl and methylene groups of alkane are involved in the exchange. The comparison of the experimentally obtained apparen t activation energies for the exchange in methyl groups (108 +/- 7 kJ mol(-1)) and methylene groups (117 +/- 7 kJ mol(-1)) with theoretical values for methane and ethane supports the assumption that the H/D exc hange for methyl and methylene groups takes place via a pentavalent tr ansition state.