Photoacoustic investigations of CO2-CH4 reaction catalyzed by nickel particles embedded into SBA15 mesopores

A photoacoustic spectroscopy technique was employed to the kinetic study of the CO2/CH4 reaction catalyzed by Ni particles embedded into the mesochannels of SBA15. The catalytic CO2/CH4 reaction was performed in a closed-circulating reactor system at various partial pressures of CO2 and CH4 (40 Torr total pressure) in the temperature range of 500-700 degrees C. The CO2 photoacoustic signal that varied with the concentration of CO2 during the catalytic reaction was recorded as a function of time by using a differential photoacoustic cell. Under the reaction conditions, the CO2 photoacoustic measurements showed the SBA15 compound used as support to be inactive for the reaction. The CO2/CH4 reaction carried out in the presence of the H-2-reduced Ni/SBA15 catalyst showed significant time-dependent changes in the CO2 photoacoustic signal, while the reaction performed in the presence of the as-prepared Ni/SBA15 catalyst did not. The CO2 photoacoustic signal obtained at early reaction times provided precise data of the CO2 disappearance rate. The rate of CO2 disappearance was observed to increase with increasing temperature in the range of 500-700 degrees C. The apparent activation energy for the CO2 consumption in the Ni/SBA15 catalyzed reaction was calculated to be 6.2 kcal/mol. Reaction orders, determined from initial rates of CO2 disappearance at various P-CO2's and P-CH4's at 700 degrees C, were found to be 0.28 for CH4 and 0.39 for CO2, respectively. The kinetic results were compared with those previously reported and were used to infer a catalytic reaction mechanism for the CO2/CH4 reaction at low pressures. (C) 2009 Elsevier B.V. All rights reserved.