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

Abstract

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 Fe_0.45Cu_0.45K_0.10/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.