Kinetic investigation of CO 2 -CH 4 reaction over Ni/La 2 O 3 catalyst using photoacoustic spectroscopy

Abstract

Ni/La 2 O 3 with a high dispersion was prepared by reduction of LaNiO 3 perovskite oxide to examine the catalytic activity for the CO 2 -CH 4 reaction. The Ni/La 2 O 3 catalyst was found to be highly active for the reaction. The ratios of H 2 /CO were measured in a flow of the reaction mixture containing CO 2 /CH 4 /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 CO 2 /CH 4 /N 2 by using a photoacoustic spectroscopy technique. The CO 2 photoacoustic signal varying with the concentration of CO 2 during the catalytic reaction was recorded as a function of time. Rates of CO 2 disappearance in the temperature range of 550-700 °C were obtained from the changes in the CO 2 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 CO 2 and CH 4, the reaction orders were determined to be 0.43 with respect to CO 2 and 0.33 with respect to CH 4. The kinetic results were compared with those reported previously and used to infer a reaction mechanism for the Ni/La 2 O 3 -catalyzed CO 2 -CH 4 reaction.