In situ studies of surface of NiFe2O4 catalyst during complete oxidation of methane

NiFe2O4 with an inverse spinel structure exhibits high activity for a complete oxidation of methane at 400 degrees C-425 degrees C and a higher temperature. The surface of the catalyst and its adsorbates were well characterized with ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ infrared spectroscopy (IR). In situ studies of the surface of NiFe2O4 using AP-XPS suggest the formation of methoxy-like and formate-like intermediates at a temperature lower than 200 degrees C, supported by the observed vibrational signatures in in situ IR studies. Evolutions of C1s photoemission features and the nominal atomic ratios of C/(Ni + Fe) of the catalyst surface suggest that the formate-like intermediate is transformed to product molecules CO2 and H2O in the temperature range of 250-300 degrees C. In situ studies suggest the formation of a spectator,-O-lattice-CH2-O-lattice-. It strongly bonds to surface through C-O bonds and cannot be activated even at 400 degrees C. (C) 2015 Elsevier B.V. All rights reserved.