Kinetic investigation of CO₂-CH₄ reaction over Ni/La₂O₃ catalyst using photoacoustic spectroscopy

Ni/La₂O₃ with a high dispersion was prepared by reduction of LaNiO₃ perovskite oxide to examine the catalytic activity for the CO₂-CH₄ reaction. The Ni/La₂O₃ catalyst was found to be highly active for the reaction. The ratios of H₂/CO were measured in a flow of the reaction mixture containing CO₂/CH₄/Ar using an on-line gas chromatography system operated at 1 atm and found to be varied with temperature between 0.66 and 1 in the temperature range of 500-800 °C. A kinetic study of the catalytic reaction was performed in a static reactor at 40 Torr total pressure of CO₂/CH₄/N₂ by using a photoacoustic spectroscopy technique. The CO₂ photoacoustic signal varying with the concentration of CO₂ during the catalytic reaction was recorded as a function of time. Rates of CO₂ disappearance in the temperature range of 550-700 °C were obtained from the changes in the CO₂ photoacoustic signal at early reaction stage. The plot of ln rate vs. 1/T showed linear lines below and above 610 °C. Apparent activation energies were determined to be 10.4 kcal/mol in the temperature range of 550-610 °C and 14.6 kcal/mol in the temperature range of 610-700 °C. From the initial rates measured at 640 °C under various partial pressures of CO₂ and CH₄, the reaction orders were determined to be 0.43 with respect to CO₂ and 0.33 with respect to CH₄. The kinetic results were compared with those reported previously and used to infer a reaction mechanism for the Ni/La₂O₃-catalyzed CO₂-CH₄ reaction.