ZIF-8-Derived Highly Active Single-Atom Iron Catalysts Towards Catalytic Transfer Hydrogenation Of Furfural

The utilization of biomass instead of fossil resources to produce fuels and chemicals has recently emerged as a hot research topic.Furfural is probably one of the most important biomass-derived chemicals.It is highly active,possessing abundant functional groups that can be converted into various oxygenated fuel molecules and chemicals.Furfuryl alcohol,which is obtained by selective hydrogenation of furfural,is one of the most important derivatives of furfural.The traditional industrial production of furfuryl alcohol requires highly polluted Cr-containing catalysts.It is of great significance to develop a green,environmental friendly,and highly active catalyst for selective hydrogenation of furfural..In this project,the ZIF-8 metal-organic framework was successfully used as precursor to prepare highly active single-atom iron catalyst by pyrolysis with trace iron.The performance of this catalyst in catalyzing transfer hydrogenation of furfural was comparable to state-of-the-art catalytic systems.The conversion of furfural achieved96.6%at a furfuryl alcohol selectivity of 93.3%at 80 ^oC in only 3 hours.More notably,the TOF of single-atom iron catalysts was as high as 2271 h^-1,which is 191 times higher than that of Fe-phen/C-800 catalysts that previously reported by our group,strongly demonstrating that single-atom iron is much more active than iron nanoparticles.Various conventional and synchrotron radiation characterization means have been used to systematically characterize the structure of catalysts and the state of Fe atoms.At the same time,the reason of catalyst deactivation was studied in-depth and the regeneration of catalyst was successfully realized.The examination of substrate scope demonstrated that the Fe-ZIF-8-800 catalyst can selectively catalyze the CTH of the-CHO group without hydrogenation of the aromatic ring.The isotope experiments demonstrated that the transfer hydrogenation reaction is proceeded by intermolecular hydrogen transfer rather than metal-hydrogen intermediates.In addition,unique substrate adaptations were found in this subject.The catalytic transfer hydrogenation of aldehydes is inhibited when the substrate contains either primary alcohol or phenol hydroxyl groups,as the H atoms in these groups are more acidic than those in the H donors.