Zn Doping Effect on the Performance of Fe-Based Catalysts for the Hydrogenation of CO2 to Light Hydrocarbons.

Nikolay Dmitrievich Evdokimenko,Konstantin Borisovich Kalmykov,Gennady Ivanovich Kapustin,Alexander Leonidovich Kustov,Olga Petrovna Tkachenko

doi:10.3390/molecules27031065

Abstract

In this work, we studied the role of zinc in the composition of supported iron-containing catalysts for the hydrogenation of CO2. Various variants of incipient wetness impregnation of the support were tested to obtain catalyst samples. The best results are shown for samples synthesized by co-impregnation of the support with a common solution of iron and zinc precursors at the same molar ratio of iron and zinc. Catalyst samples were analyzed by various methods: Raman, DRIFT-CO, TPR-H2, XPS, and UV/Vis. The introduction of zinc leads to the formation of a mixed ZnFe2O4 phase. In this case, the activation of the catalyst proceeds through the stage of formation of the metastable wustite phase FeO. The formation of this wustite phase promotes the formation of metallic iron in the composition of the catalyst under the reaction conditions. It is believed that the presence of metallic iron is a necessary step in the formation of iron carbides—that is, active centers for the formation and growth of chain in the hydrocarbons. This leads to an increase in the activity and selectivity of the formation of hydrocarbons in the process of CO2 hydrogenation.

Highlights

It is believed that the presence of metallic iron is a necessary step in the formation of iron carbides—that is, active centers for the formation and growth of chain in the hydrocarbons
Iron oxides are responsible for the reverse water shift reaction [17,18], and iron carbides are the centers of chain formation and growth [19,20]
Various promoters are used to increase the activity and selectivity of these catalysts; as a rule, these are alkali metals. They promote the formation of iron carbides under the reaction conditions and an increase in the selectivity of the formation of light hydrocarbons, but at the same time, they prevent the adsorption of hydrogen, thereby slowing down the course of the reaction [21–23]

Summary

Introduction

The issue of reducing greenhouse gas emissions is becoming more acute.One such gas is CO2. The CO2 molecule is extremely stable; for carrying out chemical reactions, it is necessary to use a heterogeneous catalyst and high-energy reagents, for example, hydrogen [6] From this point of view, hydrogenation of CO2 on heterogeneous catalysts is a simple and convenient way to obtain synthesis gas, hydrocarbons of various structures, methanol, other alcohols, and some oxygenates [7–12]. Zinc helps to increase the activity of these catalysts in the Fischer–Tropsch process [24,25], increases the adsorption of carbon dioxide [24,26,27] and hydrogen [27,28], and increases the activity in the reverse water shift reaction [29,30]. It should be noted that zinc is one of the main components of copper-containing catalysts for the hydrogenation of CO2 to methanol, where zinc plays the role of both a structural and electronic promoter, providing high dispersion of copper and increasing the adsorption of CO2 [37–41]. We report the presence of an electronic effect due to the presence of zinc in the structure of an iron–zinc catalyst deposited on a carrier ZrO2

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Conclusion