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

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.