Rh and Ni–Fe Alloy Catalysts Supported on γ ‐Al 2 O 3 for CO 2 Methanation: A Combined Kinetic and DRIFTS Study

Catalytic CO 2 methanation offers a promising pathway for converting captured CO 2 and renewable H 2 into synthetic methane. This study presents a comparative investigation of γ ‐Al 2 O 3 ‐supported Ni–Fe alloy and Rh catalysts under identical reaction conditions, integrating parametric evaluation, power‐law kinetic modeling, and in situ DRIFTS. The optimum conditions identified as 623 K, CO 2 :H 2 :Ar = 1:6:3, and GHSV = 60 000 mL h −1 gcat −1 , where 75Ni25Fe showed higher CO 2 conversion, while 100Rh achieved nearly 100% CH 4 selectivity. Both catalysts showed stable performance over 12 h of continuous operation. Kinetic analysis revealed the positive and fractional apparent reaction orders for both CO 2 and H 2 (for 75Ni25Fe, α = 0.28 ± 0.09, and β = 0.34 ± 0.07, whereas for 100Rh, = 0.22 ± 0.06, and β = 0.56 ± 0.05), indicating nonlinear rate dependence on reactant's partial pressures. The apparent activation energy was lower for 100Rh (96 kJ mol −1 ) compared to 75Ni25Fe (114 kJ mol −1 ), reflecting its higher intrinsic activity. In situ DRIFTS revealed distinct mechanistic pathways: Ni–Fe alloy catalyst follows a formate‐mediated route, while the Rh catalyst favors RWGS followed by the CO methanation route. Overall, Rh serves as a benchmark for CH 4 selectivity, while Ni–Fe offers a cost‐effective alternative for CO 2 methanation.