Activation of small alkanes on solid acids. An H/D exchange study by liquid and solid-state NMR: The activation energy and the inhibiting effect of carbon monoxide

The regioselective hydrogen/deuterium exchange taking place between isobuta ne and acidic OH groups of strong solid acids has been investigated both by in-situ solid state H-1 MAS NMR with perdeuteroisobutane and H-ZSM5 and by liquid H-1 and H-2 NMR with isobutane on various D2O-exchanged solid acids . The activation energy of the process was estimated from the variable temp erature in-situ H-1 MAS NMR kinetic experiments. A drastic inhibition of th e hydrogen exchange was observed in all cases when carbon monoxide was pres ent which is rationalized by the interaction of CO with carbocationic react ion intermediates. (C) 1999 Academic Press.