Tuning exsolution by pore architectures of Ni@S-1 and Ni@MCM-41 in CO₂ hydrogenation

This study investigates how silica pore architecture regulates Ni exsolution, affecting product distribution in CO₂ hydrogenation. Exsolved Ni species supported on microporous silicalite-1 (S-1) and mesoporous MCM-41 are systematically compared with impregnated counterparts by correlating structure, reducibility, CO_x adsorption, in-situ CO₂-H₂ switching diffuse reflectance infrared Fourier-Transform spectroscopy (DRIFTS), and catalytic performance. Ni exsolution is pronounced in the confined micropores of S-1, where strong Ni-support interactions stabilize interfacial Ni-O-Si environments, weaken CO adsorption, and promote CO selectivity with suppressed methanation. In contrast, the larger mesopores of MCM-41 attenuate exsolution effects, resulting in minor differences between exsolved and impregnated catalysts. In-situ DRIFTS reveals that exsolved catalysts preferentially stabilize monodentate carbonate species on interfacial sites, whereas impregnated catalysts favor bidentate carbonates, with carbonate speciation and vibrational features remaining pore-dependent. Overall, pore-controlled Ni exsolution is more pronounced in microporous silica, revealing a strategy for designing methanation or reverse water-gas shift (RWGS)-selective Ni-based silica catalysts.