CO2 methanation over Ni catalysts based on ternary and quaternary mixed oxide: A comparison and analysis of the structure-activity relationships

Methanation of CO2 was studied in a high throughput reactor (Amtech SPIDER 16) over Ni catalysts supported on ternary and quaternary alumina-zirconia-titania-ceria mixed oxides, in order to compare them under industrial relevant conditions and derive indications about the structure-activity relationships and specifically the role of ceria. The samples were characterized by BET, XRD, H-2-TPR, CO-chemisorption, XPS and CO-TPD analyses. Catalytic activity was evaluated towards CO2 methanation at 5 bar pressure, temperature range of 300-400 degrees C and different Gas Hourly Space Velocities (GHSVs). The results showed that enhanced catalytic activity depends on both textural improvements (for the ternary oxide supported Ni) and reducibility and metal dispersion (for the quaternary oxide supported Ni). The comparison between both groups of catalysts revealed that addition of CeO2 to 20% Ni/Al2O3-ZrO2-TiO2 further improves the catalytic performance. The catalyst supported on a mixed oxide support with 15 wt% of ceria, titania and zirconia (the remaining 55% is alumina) exhibits the highest CO2 conversion (82%) and methane selectivity (98%) at 350 degrees C and GHSV of 4000 h(-1). The role of CeO2 as promoter is to increase Ni dispersion and stabilize the presence of beta-type NiO species which are reduced at lower temperatures. Other promoters (TiO2, ZrO2) have mainly a textural effect. Moreover, CeO2 promotes also the stability decreasing the deactivation rate of about one order of magnitude with respect to the best ternary system (Ni/C5) investigated.