CHROMIUM OXIDE-CATALYZED DISPROPORTIONATION OF CHLORODIFLUOROMETHANE - A MECHANISM STUDY

The facile dispropartionation of CHF2Cl over chrome(III) oxide-based catalysts has allowed the study of catalyst activation and disproportionation as separate processes. Using both a conventional plug-flow microreactor and a TAP reactor, we have found evidence that chrome oxides, in the presence ofCHF2Cl, undergo at least two separate surface transformations before becoming catalytically active toward disproportionation. The first transformation involves a reductive deoxygenation of high-valent surface-Cr species resulting in the formation of CO2 and other oxidized products. This reduced surface then reacts with CHF2Cl to form CO and a halogenated, catalytically active surface. It is proposed that catalysis occurs on coordinatively unsaturated halogenated Cr3+ active sites. An increase in Lewis acidity of the catalyst surface was shown to accompany each transformation step. A brief kinetic study of the disproportionation gave evidence that the reaction does not proceed by a Rideal-Eley mechanism. Examination of initial product distributions, arising from a CHF3-activated catalyst, gave evidence that is consistent with a monomolecular halogen-exchange mechanism. © 1993 Academic Press, Inc.