Carbon dioxide hydrogenation to methane over silica supported nickel catalysts in a differential reactor and kinetic model development

Abstract

Development of a kinetic model for CO2 methanation over a commercial nickel catalyst was performed to consider pathways of CO2 conversion via Sabatier and RWGS reactions. H2/CO2 ratio in the feed gas composition was varied at the stoichiometry of the Sabatier reaction assuming a fictitious CO2 conversion of 0 to 0.7. Non-stochiometric gas feeding and the addition of product gases, i.e., methane and steam, were also considered to examine reaction orders and inhibition effects. The kinetic tests were carried out at 300–350 °C and 0.1–0.9 MPa. GHSV corresponded to 37,494 h-1. The stable activity was achieved by forcibly stressing the catalyst under the equilibria at 500 °C for 35 h. The kinetic measurements were conducted at an isothermal differential fixed bed reactor in the absence of heat and mass transport limitations. The methanation reaction was first fitted with a power law (PL, PL-H2O, PL-WI, PL-OH) and LH approaches by considering the Sabatier reaction. Then, the RWGS reaction was added to consider CO formation using power law models. The least-square method was performed to minimize the residues between experimented and predicted reaction rate values for prediction kinetic parameters. The models were discriminated under the lowest value of the Akaike information criterion (AIC) and Bayesian information criterion (BIC). The results showed a better fitting of experimental observations by using the LH expression with the formation of formyl as RDS and power law model with inhibiting influence of water.