Reaction kinetics studies and analyses of isobutane conversion over H-mordenite and β-zeolite

Reaction kinetics data were collected for the conversion of isobutane over H-mordenite and β-zeolite, under conditions where reaction was initiated primarily by addition of isobutylene to the feed and where stable catalyst performance was achieved. We successfully extended our kinetic model, previously developed to describe the conversion of isobutane over USY, to describe the reaction kinetics data of the present study. Catalyst performance for isobutane conversion is controlled primarily by composite activation energies, defined in terms of the energies of transition states relative to gas-phase reactants. The composite activation energies of monomolecular activation steps are lower by about 20–25 kJ mol−1 over H-mordenite and β-zeolite compared to USY. In addition, the composite activation energies for hydride transfer and oligomerization/β-scission steps are lower by about 20–30 kJ mol−1 over H-mordenite and β-zeolite compared to USY. This result suggests that the same zeolitic interactions responsible for stabilizing the transition states for monomolecular activation are also important for stabilizing the transition states for hydride transfer and oligomerization/β-scission reactions. Our results also suggest that the heats of adsorption of olefins are more exothermic on H-mordenite and β-zeolite compared to USY, again implying that the same interactions responsible for stabilizing the transition states for monomolecular and bimolecular reactions are also important in stabilizing adsorbed reaction intermediates.