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), and HFC-134a (CF3CFH2). These refrigerants are among those in a new class which contain hydrogen and fluorine substituents rather than fluorine and chlorine. This catalyst is generally non-specific and is used to oxidize carbon monoxide, hydrogen, and a variety of hydrocarbons and nitrogen compounds in heated burners, however, its activity toward refrigerants has been unpredictable. For our application, the catalyst is used in a heated burner in the closed-air environment on board submarines. In the process of optimizing the burner conditions for maximal activity toward airborne hydrocarbon contaminants and minimal activity toward refrigerants, we discovered enhanced and selective oxidative decomposition of these refrigerants in a group of recently-formulated catalyst lots which were manufactured with a higher percentage of ‘fines’. We attribute the increase in oxidative decomposition to an increase in adsorption of the refrigerants on the recently-formulated catalyst. We also observed some enhancement of activity toward CO on the recently-formulated catalyst. In addition to absorption isotherm measurements, we present several characterizations of the catalysts including scanning electron microscopy, elemental analysis, X-ray photoelectron spectroscopy, and temperature-programmed reduction.