화학공학소재연구정보센터
Journal of Catalysis, Vol.283, No.1, 75-88, 2011
Kinetic modeling of the total oxidation of propane over Cu- and Ce-based catalysts
The mechanism of the total oxidation of propane over alumina supported CuO, CeO(2), and CuO-CeO(2) is studied by means of Temporal Analysis of Products in the temperature range 623-873 K. A reaction scheme is proposed for the total oxidation of propane with O(2), as well as for the separate reduction and oxidation steps. For the reduction of the catalyst with propane, four elementary steps are considered as kinetically significant: (1) reversible associative propane sorption, (2) irreversible dissociative propane adsorption involving a methylene C-H bond breaking and ultimately forming CO(2)*(,s), (3) desorption of CO(2)*('s) to CO(2), and (4) dissociation of CO(2)*('s) to CO*(,)s and O*('s), and recombination of CO*('s) and O*('s) to CO(2)*('s), For the oxidation of the catalyst with O(2), two elementary steps are considered as kinetically significant: (1) reversible dissociative adsorption of O(2) on two reduced active sites and (2) diffusion of lattice O atoms from the surface to the bulk and vice versa. An adequate description of the full mechanism, i.e., in the presence of propane and O(2), can only be obtained by considering additional steps, which distinguish between lattice oxygen atoms at the surface, O*('s), and weakly bound oxygen atoms, O(weak). Apart from estimating the different kinetic parameters, a new approach to determine the initial concentration of reduced active sites is presented. CuO-CeO(2)/gamma-Al(2)O(3) is a more efficient total oxidation catalyst than the corresponding single metal oxides. The activation energy for the first C-H bond activation in propane over the CuO-CeO(2)/gamma-Al(2)O(3) amounts to 62 kJ mol(-1) and is significantly lower than the activation energies over the single metal oxides, i.e., 95 kJ mol(-1) for CuO/theta-Al(2)O(3) and 126 kJ mol(-1) for CeO(2)/gamma-Al(2)O(3). The redox activity of CuO-CeO(2)/gamma-Al(2)O(3) is created by the ability to reduce and re-oxidize both CuO and CeO(2), which is enhanced by a strong interaction between these phases. (C) 2011 Elsevier Inc. All rights reserved.