Active and stable Ni based catalysts and processes for biogas upgrading: The effect of temperature and initial methane concentration on CO2 methanation

CO2 hydrogenation to methane (CO2 methanation) is gaining increasing interest asa major chemical synthesis process for chemical storage of fluctuating renewable energy and producing synthetic natural gas by providing an effective process for biogas upgrading. In this study, a series of 12 and 20wt% Ni/Al2O3 catalysts, either unpromoted or promoted by 0.5wt% Ru, were prepared by the incipient wetness method for the CO2 methanation reaction from a feed of pure CO2 or biogas. The catalysts were characterized by N2 physisorption, XRD, TPR and H2 chemisorption. The activity for the 12wt% Ni catalyst increased continuously in the temperature range from 250°C to 400°C. Increasing the Ni loading and Ru promotion greatly improved the activity of the catalyst. At 350°C, the highest CO2 conversion of 82% and CH4 selectivity of 100% was achieved over the 20Ni0.5Ru/Al2O3 catalyst. Thereafter, methanation of a simulated biogas mixture was investigated over the 20Ni/Al2O3 and 20Ni0.5Ru/Al2O3 catalysts. The results showed that the CO2 conversion and CH4 selectivity were only mildly affected by the feed composition. Furthermore, the stability of the catalysts was similar regardless of the feed composition. This study demonstrates that high purity CH4 can be achieved from a biogas feed over our Ni based catalysts.