Catalytic Activity of Ni-Based Oxygen-Carriers for Steam Methane Reforming in Chemical-Looping Processes

摘要

Chemical-looping technology has been suggested as one of the most promising technologies for reducing the cost of CO_2 capture using fossil fuels. This technology involves the use of an oxygen-carrier, which transfers oxygen from air to the fuel avoiding the direct contact between them. Oxygen carriers based on nickel have been the most extensively analyzed in the literature because of their good performance working at high temperatures (900-1100 ℃). It is well-known that Ni catalyzes steam methane reforming (SMR) and water-gas shift (WGS) reactions, which are produced both in chemical-looping combustion (CLC) and chemical-looping reforming (CLR) processes. In this work, the catalytic activity of two Ni-based oxygen-carriers prepared by impregnation, NiO_(18)-αAl_2O_3 and NiO_21-γAl_2O_3, with respect to SMR and WGS reactions, have been determined in a fixed-bed reactor at different operating conditions. The catalytic activity was similar for both oxygen-carriers but lower than that exhibited by conventional Ni catalysts. Nevertheless, the catalytic effect was of great relevance to achieve complete CH, conversion in CLC and CLR systems. In addition, it was found that die catalytic activity of the oxygen-carriers frame SMR depended on the oxidation degree of the oxygen-carrier. This fact must be considered when the SMR takes place simultaneously to the reduction of NiO.