Photoacoustic investigations of CO 2–CH 4 reaction catalyzed by nickel particles embedded into SBA15 mesopores

Abstract

A photoacoustic spectroscopy technique was employed to the kinetic study of the CO 2/CH 4 reaction catalyzed by Ni particles embedded into the mesochannels of SBA15. The catalytic CO 2/CH 4 reaction was performed in a closed-circulating reactor system at various partial pressures of CO 2 and CH 4 (40 Torr total pressure) in the temperature range of 500–700 °C. The CO 2 photoacoustic signal that varied with the concentration of CO 2 during the catalytic reaction was recorded as a function of time by using a differential photoacoustic cell. Under the reaction conditions, the CO 2 photoacoustic measurements showed the SBA15 compound used as support to be inactive for the reaction. The CO 2/CH 4 reaction carried out in the presence of the H 2-reduced Ni/SBA15 catalyst showed significant time-dependent changes in the CO 2 photoacoustic signal, while the reaction performed in the presence of the as-prepared Ni/SBA15 catalyst did not. The CO 2 photoacoustic signal obtained at early reaction times provided precise data of the CO 2 disappearance rate. The rate of CO 2 disappearance was observed to increase with increasing temperature in the range of 500–700 °C. The apparent activation energy for the CO 2 consumption in the Ni/SBA15 catalyzed reaction was calculated to be 6.2 kcal/mol. Reaction orders, determined from initial rates of CO 2 disappearance at various P C O 2 ’s and P C H 4 ’s at 700 °C, were found to be 0.28 for CH 4 and 0.39 for CO 2, respectively. The kinetic results were compared with those previously reported and were used to infer a catalytic reaction mechanism for the CO 2/CH 4 reaction at low pressures.