Metal–support interactions in Fe–Cu–K admixed with SAPO-34 catalysts for highly selective transformation of CO2 and H2 into lower olefins

Direct conversion of greenhouse gas carbon dioxide (CO2) into lower olefins (ethylene, propylene and butene) provides an appealing approach to tackle CO2 emission challenges. Admixed catalysts composed of metal/metal oxides and SAPO-34 have been widely used for catalytic CO2 hydrogenation to lower olefins. However, interactions between metal/metal oxides and SAPO-34 remain obscure. Here, a novel family of admixed catalysts composed of Fe–Cu–K and SAPO-34 (Fe–Cu–K/SAPO) is developed for efficient catalytic CO2 hydrogenation to lower olefins, which can achieve 49.7% CO2 conversion and 62.9% selectivity of lower olefins, with CO selectivity <10%, over the optimal Fe0.45Cu0.45K0.10/SAPO-34 (with 1/1 mass ratio) catalyst. This exceptional performance is attributed to the change of structures, reducible properties and mass transfer resulting from strong interactions between metal/metal oxides and zeolites. First, SAPO-34 promotes the exposure of the active Cu–Fe (100) plane via disrupting the oriented growth process of Fe–Cu–K. Second, SAPO-34 boosts the reducible properties of Fe–Cu–K/SAPO-34, promoting CO2 adsorption and dissociation and thus resulting in the formation of θ-Fe3C active sites for hydrocarbon formation. Finally, the main mass transfer method of long-chain hydrocarbons/methanol from Fe–Cu–K to SAPO-34 is gas diffusion, and the dispersion of Fe–Cu–K over SAPO-34 accelerates such gas diffusion. This study provides a potential novel pathway to solve the challenge of efficiently converting CO2 into lower olefins and clarifies the effect of strong interactions between metal/metal oxides and zeolites on activities.