Efficient Conversion of CO ₂ to Hydrocarbons over Carbon-Confined InO x -ZnZrO x @C and (Ga,Al)Beta Tandem Catalysts

The hydrogenation of CO2 into high-value hydrocarbons is an effective strategy to mitigate the adverse ecological and environmental impacts of greenhouse gases and realize the resource utilization of CO2. However, owing to the high chemical inertness of CO2 and the presence of multiple competing reaction pathways, the efficient conversion of CO2 into hydrocarbons remains a major challenge. In this work, a series of carbon-confined composite metal oxides InOx-ZnZrOx@C with different indium contents were prepared using the metal–organic framework UiO-66 as both the zirconium and carbon source via a liquid deposition-pyrolysis method. (Ga,Al)Beta zeolites modified by gallium isomorphous substitution were prepared by a postsynthesis method, and tandem catalysts were constructed by physically mixing InOx-ZnZrOx@C with (Ga,Al)Beta zeolites. The catalytic performance of the tandem catalysts for CO2 hydrogenation to butane, suitable as clean fuels and high-value aromatics, was systematically evaluated. The effects of indium content and oxygen vacancy density in the composite oxides, as well as the acidity of the zeolites, on the catalytic performance were comprehensively investigated. The results demonstrate that carbon confinement effectively suppresses the aggregation of composite metal oxide nanoparticles in InOx-ZnZrOx@C, thereby increasing the number of exposed active sites. Indium modification of ZnZrOx@C generates a higher density of oxygen vacancies, while carbon confinement markedly enhances electron transfer, as well as the adsorption, activation, and hydrogenation of CO2 over the metal oxides. Simultaneously, the Brønsted acid strength is weakened, and GaO+ species with strong Lewis acidity are generated by Ga isomorphous substitution modification. The synergistic interaction between metal sites and acid sites provided by InOx-ZnZrOx@C and (Ga,Al)Beta zeolites, respectively, effectively promotes hydrogenation of CO2 to aromatics and suppresses the reverse water–gas shift reaction (RWGS). A butane and aromatics total selectivity of 83.3% at a CO2 conversion of 18.6% was achieved over the optimized 5InOx-ZnZrOx@C/(Ga,Al)Beta-S2 catalyst, with undesirable CO selectivity as low as 7.5%, and the catalyst maintained excellent catalytic stability after 100 h of reaction. This catalyst system has potential for application in the conversion of CO2 to butane and aromatics that can be used as clean fuels and chemicals.