Anchored Fe3 and Ni3 Sites on Mo2CO2-v MXene for Selective Hydrodeoxygenation of Biomass-Derived Carboxylic Acids to Alkanes and Alcohols

Catalytic hydrodeoxygenation (HDO) of biomass-derived carboxylic acids is a critical process for upgrading bio-oil to value-added fuels and chemicals, but developing efficient catalysts remains a significant challenge. Single-cluster catalysts (SCCs) have exhibited an unexpected performance in heterogeneous catalysis involving complex redox reactions. Herein, we report a series of triatomic SCCs anchored on oxygen-vacancy-containing Mo₂CO₂ MXene (Mo₂CO_2-v) for the HDO of acetic acid (AA) using density functional theory calculations and microkinetic modeling, the applicability of proposed SCCs to other carboxylic acids has also been verified. Through screening, Fe₃/Mo₂CO_2-v and Ni₃/Mo₂CO_2-v are identified as promising catalysts for selective ethane and ethanol production, respectively, with turnover frequencies significantly exceeding that of the noble metal Ru(0001) surface under identical conditions. The unique μ₂-η²(C,O):η¹(O) and μ₂-η¹(O):η¹(O) adsorption configurations of AA on Fe₃ and Ni₃ active centers enable direct cleavage of C–OH bond, bypassing the unfavorable O–H dissociation pathway and being thus responsible for the efficient conversion. Electronic structure analysis attributes their high activity to strong orbital interactions between metal clusters and adsorbates and synergetic metal–support electron regulation, which promote C–OH activation and selective hydrogenation. Furthermore, we verified that heteroatom doping can further improve the activity and selectivity of Fe₃/Mo₂CO_2-v and proposed corresponding activity descriptors, demonstrating the tunability for the catalytic performance of the proposed SCCs. This work not only provides promising catalyst candidates for HDO upgrading of carboxylic acids but also could guide the rational design of high-performance catalysts for biomass valorization.