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

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 CO2 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 CO2 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 (C2–C4=) 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·gcat–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% CO2 conversion. The TPD results and reaction performance reveal that the Fe–Co (R) catalyst has higher adsorption for weakly adsorbed CO2, H2, and CO, which results in higher CO2 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 CO2, H2, 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.