Selective catalytic activity toward hydrofluorocarbon refrigerants in mixed oxides of manganese and copper

We report selective activity of an oxidative catalyst made of manganese and copper oxides toward two ozone-safe refrigerants, HFC-236fa (CF3CH2CF3), a nd HFC-134a (CF3CFH2). These refrigerants are among those in a new class wh ich contain hydrogen and fluorine substituents rather than fluorine and chl orine. This catalyst is generally non-specific and is used to oxidize carbo n monoxide, hydrogen, and a variety of hydrocarbons and nitrogen compounds in heated burners, however, its activity toward refrigerants has been unpre dictable. For our application, the catalyst is used in a heated burner in t he closed-air environment on board submarines. in the process of optimizing the burner conditions for maximal activity toward airborne hydrocarbon con taminants and minimal activity toward refrigerants, we discovered enhanced and selective oxidative decomposition of these refrigerants in a group of r ecently-formulated catalyst lots which were manufactured with a higher perc entage of 'fines'. We attribute the increase in oxidative decomposition to an increase in adsorption of the refrigerants on the recently-formulated ca talyst. We also observed some enhancement of activity toward CO on the rece ntly-formulated catalyst. in addition to absorption isotherm measurements, we present several characterizations of the catalysts including scanning el ectron microscopy, elemental analysis, X-ray photoelectron spectroscopy, an d temperature-programmed reduction. (C) 2000 Published by Elsevier Science B.V. All rights reserved.