Hydrogenation of CO2 to light olefins over Ga2O3-ZIF-8 tandem catalyst

Abstract

A novel composite catalyst constructed based on Zeolitic Imidazolate Frameworks-8 (ZIF-8) is developed, which can directly convert CO 2 to light olefins without the participation of zeolites , providing a new idea for the development of CO 2 hydrogenation catalysts. Under the optimal conditions, CO 2 conversion of 20.2 % and C 2 = -C 4 = selectivity of 73.6% in all hydrocarbons were achieved over the Ga 2 O 3 -ZIF-8 catalyst. At the same time, to address the problem of poor thermal stability of ZIF-8, we modified it with the rare earth element La , which not only improved its catalytic stability from 30h to 50h, but also increased the conversion of CO 2 . • Ga 2 O 3 -ZIF-8 shows high catalytic activity in the tandem hydrogenation of CO 2 to light olefins . • The ZIF-8 was modified by metal La to improve the thermal stability of Ga 2 O 3 -ZIF-8 catalyst. • The thermal decomposition temperatures of ZIF-8 and La-ZIF-8 were simulated by molecular dynamics theory. Tandem catalysts composed of metal oxides and zeolites have demonstrated significant potential for the hydrogenation of CO 2 to light olefins. However, their development is hindered by the competing reverse water–gas shift reaction and carbon accumulation on the zeolite surface. To address these challenges, we developed a series of innovative tandem catalysts by substituting conventional zeolites with ZIF-8. Our research primarily focused on examining the effects of metal species and content, as well as the particle size of ZIF-8, on catalytic performance. Notably, we achieved a CO 2 conversion of 20.2 % and a light olefins selectivity of 73.6 % using a catalyst with 20 % Ga 2 O 3 content and a ZIF-8 particle size of 100 nm at a reaction temperature of 340 °C and pressure of 3.0 MPa. In order to improve the stability of the catalyst, ZIF-8 was modified with La to improve its thermal stability. A CO 2 conversion of 23.5 % and a light olefins selectivity of 66.5 % were maintained after 50 h of continuous reaction. While the catalytic activity of La-modified catalysts is slightly lower than that of unmodified ones, their superior stability makes them more suitable for thermal catalytic hydrogenation of CO 2 . Various characterizations and theoretical calculations revealed that La modification not only enhanced the thermal stability of catalyst but also improved its adsorption and activation capabilities for the reacting gases. Furthermore, the reaction mechanism of CO 2 hydrogenation to light olefins was investigated by in-situ diffuse reflectance Fourier transform infrared spectroscopy. This study provides a technical foundation for designing efficient catalysts based on metal–organic frameworks in the field of carbon dioxide thermal catalytic conversion.