Comparative Study of Short-Chain Olefins Synthesis via CO₂ Hydrogenation over Iron-Containing Double Metal Cyanide-Derived Catalysts

Abstract

In this article, we prepared a series of K-promoted double metal cyanide (DMC) catalysts consisting of iron with a late 3d transition metal (Mn, Co, Cu, and Zn) using a single-step conventional precipitation method and examined them for CO 2 value addition to short-chain olefins via modified Fischer–Tropsch route. Several ex situ/in situ combined with temperature-programmed desorption (TPD) experiments were carried out to identify the species in the catalysts and evaluate the adsorption/desorption characteristics of the reduced catalysts. The CO 2 conversion for bimetallic catalysts increases in the following order: Fe–Mn (R): 24.85% < Fe–Zn (R): 28.60 < Fe–Cu (R): 29.40% < Fe–Co (R): 39.10% whereas selectivity of the short-chain olefins (C 2 –C 4 = ) in hydrocarbons decreases in the following order: Fe–Mn (R): 56.1% > Fe–Cu (R): 55.4% > Fe–Zn (R): 50.8% > Fe–Co (R): 44.3%, at 20 bar pressure, 320 °C temperature, and a gas hour space velocity (GHSV) of 3600 mL·g cat –1 ·h –1 . Remarkably, during the optimization of the reaction conditions, short-chain olefins selectivity over the Fe–Mn (R) catalyst unprecedently reached up to 63.8% in hydrocarbons with 30.56% CO 2 conversion. The TPD results and reaction performance reveal that the Fe–Co (R) catalyst has higher adsorption for weakly adsorbed CO 2, H 2, and CO, which results in higher CO 2 conversion, lower CO, and higher hydrocarbon selectivity with a lower O/P ratio. Contrarily, the Fe–Mn (R) catalyst exhibits opposite reaction outcomes to the Fe–Co (R) catalyst owing to its lower adsorption for weakly adsorbed CO 2, H 2, and CO. These findings shed light on how the conversion of reactant and product distribution is affected by the adsorption/desorption characteristics of the catalysts for the reactant and important intermediates.

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