3D printed Ni–Mn-modified rice husk derived mesoporous SiO₂ with an optimized Ni/Mn ratio for enhanced low-temperature CO₂ methanation: Experimental and theoretical studies

Highly efficient 3D printed monometallic Ni and bimetallic Ni-Mn catalysts supported on biowaste-derived silica for CO₂ methanation were developed. The optimal Ni-Mn ratio and the presence of moderate-strength basic sites promoted high CO₂ conversion to methane. Ni-Mn catalysts show higher catalytic activity and higher selectivity to methane. The 3D-7Ni3Mn/MS catalyst achieved stable CO₂ conversion of 83 % at 290 °C with 99.5 % methane selectivity. The operando DRIFT spectroscopic investigations suggest that both *CO and HCOO* species are key intermediates of methane formation on Ni and Ni-Mn catalysts. These observations are supported by DFT calculations, revealing that the synergism between Ni and Mn facilitates CH₄ formation from CO₂, which could result in higher catalytic activity. The long-term stability test demonstrated that the activity and selectivity of the 3D-7Ni3Mn/MS catalyst was preserved in 31 h reaction time. The excellent catalytic performance and stability of 3D-printed catalysts highlight their potential as efficient, low-temperature catalysts for CO₂ methanation. • 3D printed Ni–Mn catalysts supported on biowaste-derived mesoporous silica. • Optimal Ni–Mn ratio and moderate-strength basic sites promoted high CO₂ conversion. • Mn facilitates CH₄ formation from CO₂ by enhancing H₂ dissociation on Ni particles. • 3D-printed catalysts show superior activity in low-temperature CO₂ methanation; • Experimental and theoretical approaches for understanding the reaction mechanism.