Trade-offs in stability and activity: A study of ordered mesoporous alumina and γ-Al2O3 supported Ni catalysts for CO2 methanation

A series of K-Ni-gamma-Al2O3 samples containing 15 wt.% Ni and varying potassium loadings (0-10 wt.%) were synthesized via incipient wetness impregnation and evaporation-induced self-assembly (EISA) for CO2 methanation. The latter method resulted in ordered mesoporous alumina (OMA) catalysts exhibiting superior CO2 conversion, CH4 selectivity, and thermal stability compared to their gamma-Al2O3-supported counterparts. The 0.5K15NiOMA catalyst demonstrated the highest performance, achieving 85% CO2 conversion at 450 degrees C under atmospheric pressure, 15% higher than the unpromoted 15NiOMA catalyst. Under high-pressure conditions (450 degrees C, 9 atm, and 180 L-N g(cat)(-1) h(-1) GHSV), the 0.5K15NiOMA catalyst achieved a CO2 conversion of 94%. Long-term stability tests over 150 h at 300 degrees C showed no deactivation, maintaining a stable CO2 conversion of 38% and CH4 selectivity of 84%. In contrast, gamma-Al2O3-supported catalysts demonstrated higher turnover frequencies despite their lower methane reaction rates. For example, at 350 degrees C, 0.5K15Ni/Al2O3 achieved a TOF of 1.00 s(-1), almost double than its unpromoted counterpart and over double the TOF of 0.5K15NiOMA. This suggests that the higher surface availability of potassium in impregnated catalysts enhances CO2 adsorption, compensating for the partial blockage of nickel sites. These results highlight the trade-offs between stability and activity, with OMA supports excelling in long-term high-temperature applications and gamma-Al2O3 supports offering a cost-effective solution with simpler preparation methods for large-scale CO2 methanation.