Product selectivity controlled by the nano-environment of Ru/ZSM-5 catalysts in nonthermal plasma catalytic CO₂ hydrogenation

Nonthermal plasma (NTP) systems combined with the supported metal catalyst is a promising method to enable CO₂ valorisation under mild conditions. However, insight into the relationships between the catalyst microstructure and the catalytic performance under NTP conditions is still lacking. Herein, Ru nanoparticles (NPs) on ZSM-5 zeolites with different zeolite morphologies (i.e., nanocrystals, nanosheets and conventional large crystals) and Ru NPs locations (i.e., externally supported, internally encapsulated and combination of the two) obtained by different preparation methods including encapsulation and impregnation, and combination of both approaches were investigated comparatively using NTP-catalytic CO₂ hydrogenation. The results revealed that the performance of the NTP-catalysis depends on the structure of the catalysts significantly. Specifically, ZSM-5 nanocrystal and nanosheet promoted the formation of small and highly dispersed Ru NPs (with the average particle diameters of 9–15 nm), which showed the strong interaction with CO molecule and promoted the selective CO₂ conversion to CH₄. Regarding the location of the Ru NPs, the accessibility of Ru NPs to the plasma-induced energetic species was rather important at lower input energies. Conversely, at higher input plasma energies, the intrinsic property of the Ru NPs determines the catalytic performance, and thus the 1%Ru(in) catalyst containing internally encapsulated Ru showed high CO₂ conversion of ∼93% and CH₄ selectivity of ∼85%, respectively. Importantly, higher input energies led to the formation of C₂H₆ via gas phase CH₄ coupling reactions.