METHANE COMBUSTION OVER COPPER CHROMITE CATALYSTS

A study of the activity and durability of two different copper chromit e catalysts in methane combustion is presented. The catalysts, a massi ve (CAT-E) and a supported (CAT-I) copper chromite, were characterized by different techniques in order to investigate morphological propert ies (N-2 adsorption), crystalline structure (X-ray diffraction, XRD) a nd surface composition (X-ray photoelectron spectroscopy, XPS). Among the different crystalline phases identified, CuCr2O4 spinel represente d the common phase in both the catalysts. The Cr-VI/Cr-III surface rat io was almost the same for the two catalysts, while the Cu-II/Cu-I sur face ratio was much higher on the massive catalyst than on the support ed one. The activity for CH4 combustion was studied in the temperature range 300-700 degrees C at constant CH4 : air ratio of 1 : 30 and con stant methane content, 1.2%. The activity was higher for CAT-I and CAT -E showed better stability. A kinetic study from the catalytic data, c ollected at different contact times in the interval 0.047-0.315 s as a function of temperature, provided a value of about 110 kJ/mol for the activation energy. This value was obtained for various degrees of met hane converted for the two catalysts. The reaction rates were between 10(-3) and 10(-4) (mol(CH4))(conv)/(g h) in the temperature interval 5 50-700 degrees C, for both the catalysts.