Facile Generation of Atomically Confined Hafnium Active Sites on Halloysite-Nanotube for the Highly Efficient Catalytic Transfer Hydrogenation of Levulinic Acid

The sluggish kinetic of the hydrogen transformation reaction is a great challenge for the development of efficient catalytic transfer hydrogenation (CTH) reaction system for the upgrading of biomass-derived platform molecules. In this contribution, for the first time, a single-atom hafnium catalyst has been developed by a facile and green self-assembly method at room temperature (Hf@HNTs). Especially, the Hf(1.7)@HNTs delivered an impressive catalytic performance for the CTH of levulinic acid (LvA) to gamma-valerolactone (GVL) with high turn-over frequency (TOF) of 43.1 h-1, considerably exceeding that on the bulk HfO2 and state-of-art Hf-based catalysts. Experimental and density functional theory (DFT) studies revealed that Hf(1.7)@HNTs possessed unsaturated-coordinated and atomically-dispersed Hf-O Lewis acid-base pairs, which favored the adsorption and activation of LvA. Moreover, DFT calculations explicitly demonstrated that the energy barriers for the hydrogen transformation reactions between the LvA and hydrogen donor were significantly reduced on the Hf(1.7)@HNTs than that of HfO2.