Selective Hydrogenation of CO2 into Ethene and Propene over a GaZrOx/H-SAPO-17 Composite Catalyst

Hydrogenation of CO2 into value-added light olefins is a promising route to achieve carbon recycling. Regulation of light olefins distribution and promotion of target olefins formation are highly important to improve carbon utilization efficiency, but rather challenging. Herein, we designed a series of GaZrOx/H-SAPO-17 composite catalysts, which show the C2=–C4= selectivity of 82.5% (CO free), with those of CH4 and C20–C40 of only 2.5 and 10.2% in hydrocarbons, respectively, at a CO2 conversion of 9.0% at 375 °C and 1.5 MPa. In particular, ethene and propene accounted for >84% of C2=–C5= alkenes. Such a performance was well-maintained for at least 100 h. Temperature-/time-dependent in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), isotope labeling in situ DRIFTS, and 13C magic angle spinning NMR indicated that formate and methoxy are the dominant intermediate species for the production of methanol on GaZrOx oxide. Upon coupling with acidic zeolite, the formed methanol intermediates were rapidly converted to light olefins. The distribution of olefins in subsequent methanol conversion was strongly related to the pore structure of H-SAPO-17 zeolite. In situ UV–vis spectroscopy, in situ DRIFTS, temperature-programed surface reaction, 12C/13C methanol switching experiments, and density functional theory computations confirmed that the small supercage structure of H-SAPO-17 has a stronger steric restriction effect on the formation of bulky aromatic species with large alkyl side chains, which, hence, significantly inhibits the generation of C4+ long-chain olefins through the aromatic-based cycle.