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A study of the activity and durability of two different copper chromite catalysts in methane combustion is presented. The catalysts, a massive (CAT-E) and a supported (CAT-I) copper chromite, were characterized by different techniques in order to investigate morphological properties (N2 adsorption), crystalline structure (X-ray diffraction, XRD) and surface composition (X-ray photoelectron spectroscopy, XPS). Among the different crystalline phases identified, CuCr2O4 spinel represented the common phase in both the catalysts. The CrVI/CrIII surface ratio was almost the same for the two catalysts, while the CuII/CuI surface ratio was much higher on the massive catalyst than on the supported one. The activity for CH4 combustion was studied in the temperature range 300-700°C at constant CH4:air ratio of 1:30 and constant methane content, 1.2%. The activity was higher for CAT-I and CAT-E showed better stability. A kinetic study from the catalytic data, collected 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 methane converted for the two catalysts. The reaction rates were between 10-3 and 10-4 (molCH4)conv/(g h) in the temperature interval 550-700°C, for both the catalysts. |
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