Kinetic investigation of CO2 reforming of CH4 over Ni catalyst deposited on silicon wafer using photoacoustic spectroscopy

Abstract

The CO2-CH4 reaction catalyzed by Ni/silicon wafers was kinetically studied by using a photoacoustic technique. The catalytic reaction was performed at various partial pressures of CO2 and CH4 (50 Torr total pressure of CO2/CH4/N 2) in the temperature range of 500 - 650 °C in a static reactor system. The photoacoustic signal that varied with the CO2 concentration during the catalytic reaction was recorded as a function of time. Under the reaction conditions, the CO2 photoacoustic measurements showed the as-prepared Ni thin film sample to be inactive for the reaction, while the CO2/CH4 reactions carried out in the presence of the sample pre-treated in H2 at 600 °C were associated with significant time-dependent changes in the CO2 photoacoustic signal. The rate of CO2 disappearance was measured from the CO2 photoacoustic signal data in the early reaction period of 50 - 150 sec to obtain precise kinetic data. The apparent activation energy for CO2 consumption was determined to be 6.9 kcal/mol from the CO2 disappearance rates. The partial reaction orders, determined from the CO 2 disappearance rates measured at various PCO2's and PCH4's at 600 °C, were determined to be 0.33 for CH4 and 0.63 for CO2, respectively. Kinetic data obtained in these measurements were compared with previous works and were discussed to construct a catalytic reaction mechanism for the CO2-CH4 reaction over Ni/silicon wafer at low pressures.