Catalytic Activity of Ti-based MXenes for the Hydrogenation of Furfural

Herein we report on the catalytic activity of Ti-based MXenes (Ti₃CNT_z and Ti₃C₂T_z) for biomass transformation. MXenes were found to be active catalysts for the hydrogenation of furfural using either gaseous hydrogen or 2-propanol as solvent and hydrogen source. Both catalysts showed good activity in the conversion of furfural to furfuryl alcohol, with furfuryl ether as the main by-product. Stability tests indicated that Ti₃CNT_z is more stable than Ti₃C₂T_z against deactivation. Ab initio calculations were used to examine the hydrogenation and etherification reactions pathways and their corresponding reaction energetics on the Ti₃CNT_z MXene. The results indicate that the hydrogenation of the carbonyl bond efficiently proceeds via the heterolytic activation of hydrogen over the metal-oxygen site pair followed by the addition of the proton and hydride to the C and O atoms of the carbonyl. The subsequent hydrogenation of the unsaturated furan ring via metal bound hydrogen, however, is calculated to be much more difficult. Protons bound to the oxygen of the MXene are acidic and can also catalyze the etherification of the resulting alcohols. The bifunctional acid-metal site pairs also selectively catalyze the hydrogenolysis of the furfuryl alcohol to form 2-methyl furan.