Influence of MXene and TiO₂ on the Performance of Microalgae-Derived Ru-Based Catalysts for CO₂ Hydrogenation to Methane

Abstract

Controlling the selectivity of CO₂ hydrogenation to produce value-added fuels and chemicals is an actual challenge in catalysis research. The exact mechanisms underlying selectivity control often remain poorly understood, slowing the design of more efficient catalysts. In this study, we investigated RuO₂ nanoparticles supported on MXene or TiO₂ for CO₂ hydrogenation at atmospheric pressure. Microalgal extracts were incorporated in the synthesis to explore their influence on catalyst properties, such as surface area, morphology, and elemental distribution. Although lower surface area and less uniform RuO₂ dispersion were observed on MXenes than on TiO₂, after reductive pretreatment Ru/MXene exhibited superior catalytic activity, demonstrating that its unique textural properties and active site availability compensated for the lower surface area. A reducibility study revealed that MXene-supported catalysts undergo a more complex reduction process than those with TiO₂ as the support. Additionally, bridge adsorption sites on MXene likely contributed to the enhanced CO₂ hydrogenation activity, whereas TiO₂ seemed to present a twin CO binding environment. Higher Ru loading on MXene increased the methane selectivity and conversion, whereas lower loading favored CO formation, highlighting the importance of optimizing catalyst loading. Operando diffuse reflectance infrared Fourier transform spectroscopy analysis revealed the critical role of methoxy intermediates in affecting the catalytic pathway, suggesting the potential for tuning synthesis conditions to improve yields. A partial encapsulation of Ru on MXene enhances the catalytic performance, while the stronger SMSI effect on TiO₂ leads to complete encapsulation, reducing the catalytic efficiency. The findings underscore the promise of MXene as a support material for metal catalysts in CO₂ hydrogenation toward environmentally friendly fuel production.