On the kinetics of the co-methanation of CO and CO₂ on a co-precipitated Ni-Al catalyst

The kinetics of the gas-phase co-methanation reaction of carbon oxides over a co-precipitated 44 wt.% NiAlO_x catalyst were modelled via competitive adsorption of CO and CO₂ and the subsequent methanation of a common surface intermediate. Steady-state isotope experiments and model discrimination suggest the decomposition of a hydrogenated COH_y surface intermediate to be the kinetically relevant step in the methanation reaction. The best fit is obtained for hydroxycarbene (y = 2). The presented kinetic model is the first to explicitly describe the full coupling of CO and CO₂ transformation. It is built on the basis of CO methanation, CO₂ methanation, steam reforming, and water-gas shift experiments over a wide range of conditions. All model parameters are thermodynamically consistent and statistically relevant.