CO2 methanation over NiO catalysts supported on CaO–Al2O3: Effect of CaO:Al2O3 molar ratio and nickel loading

Abstract

This study conducted the CO2 methanation reaction over the nickel-based catalysts supported on CaO.Al2O3 with different CaO/Al2O3 molar ratios. The catalyst support was synthesized with the mechanochemical method, and the influence of nickel loading was investigated on the selected catalyst support with an appropriate CaO/Al2O3 molar ratio. According to the results, incorporating Al2O3 into the CaO increased the BET area from 5 to 196 m2 g−1. Also, the SBET of the calcined catalysts decreased with the augmentation of nickel oxide percentage from 5 to 15 wt% due to the pore blocking of the support after metal addition. Moreover, the activity of catalysts enhanced with the increment of CaO/Al2O3 molar ratio and NiO percentage, ascribed to the improvement in the reducibility of the catalysts. However, the excessive addition of CaO and nickel oxide reduced the CO2 conversion because of a significant decrease in surface area. Therefore, 10 wt% NiO/CaO.2Al2O3 catalyst possessed superior CO2 conversion (79.1%) and CH4 selectivity (98.1%) in CO2 methanation reaction at 450 °C, H2/CO2 = 4 and GHSV = 18,000 ml h−1.g−1cat. The selected sample illustrated great stability for 11 h without any remarkable change in its initial catalytic activity. The impact of GHSV on the catalytic performance of the selected catalyst was evaluated, and the outcomes exhibited that decrement in GHSV value enhanced CO2 conversion. With the increment of feed ratio (H2/CO2) from 2 to 5, CO2 conversion reached 93.3%, ascribed to the existence of adequate hydrogen to react with CO2.