Abstract:
CO
2 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
yO
4/SAPO−34 bifunctional catalysts for CO
2 hydrogenation to light olefins (C
2=~C
4=), 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, H
2-TPR, CO
2-TPD, Raman spectroscopy, and in situ DRIFTS, were employed to systematically analyze the influence of different synthesis methods on the phase structure, reducibility, CO
2 adsorption capability, and evolution of reaction intermediates of Zn
xCe
2−yZr
yO
4. 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): CO
2 conversion reaches 12.44%, the selectivity for light olefins (C
2=~C
4=) 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 CO
2-TPD results demonstrate that the catalyst prepared by the sol-gel method possesses the highest surface oxygen vacancy concentration, which facilitates CO
2 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 CO
2 hydrogenation to light olefins.