Kinetic Investigation of CO2-CH4 Reaction over Ni/La2O3 Catalyst using Photoacoustic Spectroscopy

Abstract

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 oC. 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 oC 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 oC. Apparent activation energies were determined to be 10.4 kcal/mol in the temperature range of 550-610 oC and 14.6 kcal/mol in the temperature range of 610-700 oC. From the initial rates measured at 640 oC 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