Kinetics and site requirements of ether disproportionation on γ-Al2O3

Measured rates of methyl propyl ether (MPE), an asymmetric ether, conversion on gamma-alumina at 623 K verify that hydration rates are negligible compared to disproportionation rates below 2.0 kPa of water. Steady state kinetic measurements establish that diethyl ether (DEE) disproportionation rates possess reaction orders between 0 and 1. A mechanism for DEE disproportionation in which ethanol monomers and reactive ethoxy species are the primary surface species is consistent with measured pressure dependencies. The intrinsic rate constant of DEE disproportionation is nearly identical to that of unimolecular ethanol dehydration, revealing the similarity in the rate-limiting steps of these two reactions. In-situ pyridine titration studies verify that DEE disproportionation and unimolecular ethanol dehydration possess similar site requirements and densities (0.3 and 0.2 sites nm(-2), respectively) while bimolecular ethanol dehydration occurs on a separate pool of catalytic sites. (C) 2015 Elsevier B.V. All rights reserved.