Selective Hydrogenation of CO<sub>2</sub> into Ethene and Propene over a GaZrO<sub><i>x</i></sub>/H-SAPO-17 Composite Catalyst
Lu Qin, Sen Wang, Sheng Fan, Mei Dong, Zhangfeng Qin, Jianguo Wang, Weibin Fan
Abstract
Hydrogenation of CO 2 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 GaZrO x /H-SAPO-17 composite catalysts, which show the C 2 = –C 4 = selectivity of 82.5% (CO free), with those of CH 4 and C 2 0 –C 4 0 of only 2.5 and 10.2% in hydrocarbons, respectively, at a CO 2 conversion of 9.0% at 375 °C and 1.5 MPa. In particular, ethene and propene accounted for >84% of C 2 = –C 5 = 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 13 C magic angle spinning NMR indicated that formate and methoxy are the dominant intermediate species for the production of methanol on GaZrO x 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, 12 C/ 13 C 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 C 4+ long-chain olefins through the aromatic-based cycle.