Kinetics of CO2 methanation on a Ru-based catalyst at process conditions relevant for Power-to-Gas applications

In this paper we show that a 0.5 wt.% Ru/gamma-Al2O3 catalyst is appropriate to carry out the Sabatier reaction (CO2 methanation) under process conditions relevant for the Power-to-Gas application and we provide a kinetic model able to describe the CO2 conversion over a wide range of process conditions, previously unexplored. To achieve these goals, the effects of feed gas composition (H-2/CO2 ratio and presence of diluents), space velocity, temperature and pressure on catalyst activity and selectivity are investigated. The catalyst is found stable when operating over a wide range of CO2 conversion values, with CH4 selectivity always over 99% and no deactivation, even when working with carbon-rich gas streams. The effect of water on the catalyst performance is also investigated and an inhibiting kinetic effect is pointed out. Eventually, the capacity of kinetic models taken from the literature to account for CO2 conversion under the explored experimental conditions is assessed. It is found that the kinetic model proposed by Lunde and Kester in 1973 (J. CataL 30 (1973) 423) is able to describe satisfactorily the catalyst behavior in a wide range of CO2 conversion spanning from differential conditions to thermodynamic equilibrium, provided that a new set of kinetic parameters is used. It is shown however that a better fitting can be achieved by using a modified kinetic model, accounting for the inhibiting effect of H2O on CO2 conversion rate.