Pt/HZSM-5 catalyst synthesized by atomic layer deposition for aqueous-phase hydrogenation of levulinic acid to valeric acid

A Pt/HZSM-5 catalyst was prepared by atomic layer deposition (ALD) for aqueous-phase hydrogenation of levulinic acid (LA) to valeric acid (VA). 5Pt/HZSM-5 produced with 5 cycles of Pt ALD was identified as a highly active and stable bifunctional catalyst, and a high yield of VA (91.4%) was achieved in aqueous solution. A close interaction between Pt and acid sites of HZSM-5 is favor for the selective generation of VA. The microporous structure and the acid sites of HZSM-5 were not changed after Pt ALD, and some Pt nanoparticles were located in the micropore channel of HZSM-5. This reveals that the Pt ALD has the advantage to protect the structure of zeolite. The average particle size of Pt nanoparticles, electric state of surface Pt, and surface acid sites are nearly not changed with the increase of Pt ALD cycle number. However, the ratio of Pt in the pore channel to that out of the pore decreases with the increase of ALD cycle numbers, resulting in a decrease of TOF of VA yield. For comparison, Pt nanoparticles supported on HZSM-5 were also produced by impregnation. But the pore structure of HZSM-5 was damaged, and more micropore were formed by impregnation method for Pt loading. Moreover, it exhibited very low catalytic activity, selectivity of VA, and stability.