Two-dimensional MXenes as catalytic “flying carpets” to transport biomass valorization towards new horizons: The case of furfural catalytic transfer hydrogenation over noble-metal free niobium-based carbides

The reductive conversion of biomass-derived furfural through catalytic transfer hydrogenation (CTH) over non-precious metal catalysts is regarded as a promising strategy to successfully implement the biorefinery concept. Here, we show that two-dimensional niobium carbides (MXenes) efficiently catalyze the liquid-phase CTH of furfural in the presence of 2-propanol as hydrogen donor. At 160 °C Nb2CTx and Nb4C3Tx showed remarkable initial activity values (130 and 73 h−1, respectively), exceeding the one of pure Nb2O5 (21 h−1) by factor of 6.2 and 3.5. A targeted surface characterization by acid site titrations and X-ray photoelectron spectroscopy allowed to correlate the catalytic behavior with the acidic features and the peculiar surface chemistry of Nb-MXenes species. The presence of strong acid sites in Nb2CTx was associated to high initial activity, but also to a pronounced tendency to undergo deactivation. Differently, Nb4C3Tx, despite the lower initial activity, assured 70 % of furfural conversion after 8 h and it showed good stability over six runs. This study could bring new opportunities for the rational design of advanced noble metal-free catalysts with enhanced activity for biomass valorization.