On understanding the effect of metal-support interactions on plasma-catalytic CO₂ hydrogenation over the Ru/ZrO₂ catalysts

This work investigates the effect of metal-support interactions (MSIs) on nonthermal plasma (NTP) catalytic CO₂ hydrogenation over ruthenium supported on zirconia catalysts (Ru/ZrO₂). The MSI of Ru/ZrO₂ was tuned by varying the crystalline phase of ZrO₂ (i.e., monoclinic: m-, tetragonal: t-, amorphous: am- and a mixed phase consisting of both monoclinic and tetragonal: mix-). The findings show that the variation in ZrO₂ phases tuned the MSI in the Ru/ZrO₂ catalysts, hence their CO₂ hydrogenation activity under the plasma conditions. Specifically, the Ru/mix-ZrO₂ catalyst showed the highest selectivity to CH₄ (of 97.3 %) with a CO₂ conversion of 81.3 %. Conversely, Ru/m-ZrO₂ and Ru/t-ZrO₂ were selective to CO (CO selectivity >90 %) with rather low CO₂ conversions of <14 %. Comprehensive characterisation suggests that mix-ZrO₂ optimised Ru dispersion, improved Ru proportion at the interface (Ru_if) and boosted the electronic interfacial anchoring of Ru on mix-ZrO₂. The in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) further revealed that the strong MSI between Ru and mix-ZrO₂ resulted in a stronger carbonyl binding on Ru, leading to enhanced CH₄ production on Ru/mix-ZrO₂. Findings of the work demonstrate that the MSI-based design strategies of thermal catalysis could be translated into NTP catalysis, tailoring catalysts' activity/selectivity in NTP catalytic CO₂ hydrogenation.