CO₂ synthesis of lower olefins over Zn_xCe_2−yZr_yO₄/SAPO−34 bifunctional catalyst

CO₂ hydrogenation via relay catalysis to produce high-value chemicals is one of the important pathways for achieving green and low-carbon chemical processes. This study systematically investigates the catalytic performance of Zn_xCe_2−yZr_yO₄/SAPO−34 bifunctional catalysts for CO₂ hydrogenation to light olefins （C₂⁼～C₄⁼）, with a focus on the effects of different preparation methods of metal oxides （sol-gel, co-precipitation, and hydrothermal methods） on their structural properties, surface oxygen vacancy concentration, hydrogenation capacity, and catalytic behavior. Various characterization techniques, including XRD, H₂-TPR, CO₂-TPD, Raman spectroscopy, and in situ DRIFTS, were employed to systematically analyze the influence of different synthesis methods on the phase structure, reducibility, CO₂ adsorption capability, and evolution of reaction intermediates of Zn_xCe_2−yZr_yO₄. Furthermore, the reaction temperature, pressure, gas hourly space velocity （GHSV）, mass ratio of oxide to zeolite, and coupling mode were optimized, and the generation and conversion mechanism of methanol/ketene intermediates over the bifunctional catalyst were elucidated. The results indicate that the catalyst prepared by the sol-gel method （using glucose as a complexing agent） combined with SAPO−34 zeolite via physical mixing exhibits the best catalytic performance under the conditions of 350 ℃, 4 MPa, and a GHSV of 6000 mL/(g·h): CO₂ conversion reaches 12.44%, the selectivity for light olefins （C₂⁼～C₄⁼） in hydrocarbon products is as high as 78.47%, and the selectivity for the byproduct CO is only 36.23%. In contrast, the sample prepared by the hydrothermal method shows higher CO selectivity and lower light olefin selectivity. Although the co-precipitation method can form a well-defined solid solution structure, its oxygen vacancy concentration and hydrogenation capacity are both inferior to those of the sol-gel method. Raman and CO₂-TPD results demonstrate that the catalyst prepared by the sol-gel method possesses the highest surface oxygen vacancy concentration, which facilitates CO₂ adsorption and activation. In situ DRIFTS further confirms that the oxide prepared by this method exhibits the strongest hydrogenation capability for intermediates, efficiently promoting the conversion of methanol/formate species to light olefins. This study systematically reveals the regulatory mechanism of metal oxide preparation methods on the structure and performance of ZnCeZrO_x/SAPO−34 bifunctional catalysts, providing theoretical insights and experimental support for the design of high-performance catalysts for CO₂ hydrogenation to light olefins.