Selective hydrogenation of CO2 to propene-abundant light olefins over ZnZrOx/ultra-small H-SAPO-34 crystals composite

Abstract

Significant increase of specific target olefin selectivity in CO₂ hydrogenation is not only scientifically interesting but also practically valuable because of the reduction of separation cost. Here, a new composite catalyst is fabricated with surface oxygen vacancy-abundant ZnZrO_x(H) solid solution and ultra-small H-SAPO-34(US) molecular sieve crystals. This catalyst shows a propene selectivity in hydrocarbons of 51.2 % that accounts for about 63 % of light olefins, along with a CO₂ conversion of 13.5 %, at 350 °C and 3.0 MPa. A combination of in situ spectroscopy, isotope-labelled experiments, DFT calculations, and AIMD simulations reveals that an increase of surface oxygen vacancies in ZnZrO_x(H) induces formation of a coordinatively unsaturated (Zr-O)_n-Zn-(Ov)_m configuration, which elevates Zn site electron density and enhances the electronic interaction of Zn-3d and H-1s orbitals. This promotes the H₂ dissociation and facilitates methanol intermediate formation. The ultra-small H-SAPO-34(US) crystals with a size of 100–200 nm effectively suppresses alkenes hydrogenation and subsequent aromatization in the methanol conversion process. As a result, more propene was produced.