The Electrophilicity of Surface Carbon Species in the Redox Reactions of CuO‐CeO₂ Catalysts

Abstract

Electronic metal–support interactions (EMSI) describe the electron flow between metal sites and a metal oxide support. It is generally used to follow the mechanism of redox reactions. In this study of CuO‐CeO2 redox, an additional flow of electrons from metallic Cu to surface carbon species is observed via a combination of operando X‐ray absorption spectroscopy, synchrotron X‐ray powder diffraction, near ambient pressure near edge X‐ray absorption fine structure spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy. An electronic metal–support–carbon interaction (EMSCI) is proposed to explain the reaction pathway of CO oxidation. The EMSCI provides a complete picture of the mass and electron flow, which will help predict and improve the catalytic performance in the selective activation of CO2, carbonate, or carbonyl species in C1 chemistry.

Approaching C1 Reaction Mechanisms Using Combined Operando and Transient Analysis: A Case Study on Cu/CeO2 Catalysts during the LT-Water–Gas Shift Reaction

“…Considering that there is no relation between the CO conversions and specific surface areas, we can conclude that defects are only a minor factor in determining the catalytic activity; thus, a surface too rich in defects (e.g., rods) may not be beneficial for WGS over Cu/CeO 2 . This is further supported by the observation that the absolute change in absorption upon switching from argon to reaction conditions does not correlate with the WGS activity, consistent with previous results on CO oxidation, which have shown that the Ce 3+ fraction is not correlated with activity and that the state of copper is of greater importance …”

“…Previous literature studies on Cu/CeO 2 catalysts have highlighted the importance of the copper oxidation state, ,,, which depends on both the gas-phase environment and the loading. ,, On the one hand, the interaction of metallic copper with oxygen vacancies (O vac ) was reported to enhance the reactivity, while on the other, copper was shown to have an oxidation state of +1 at the interface and to participate in the reaction, as supported by other studies, demonstrating the stability of oxidized copper under reductive conditions . In addition, a strong dependence of the state of copper on the gas phase at 180 °C was observed for 20 wt % Cu/CeO 2 , that is, mainly Cu 0 was detected during CO exposure and Cu + in the subsequent exposure to an inert gas . At low loadings, for example, 1 wt % Cu/CeO 2 , the catalyst behaves differently, as rather Cu + is observed under a CO atmosphere, which is then further oxidized to Cu 2+ on switching to He, indicative of electronic metal–support interactions.…”

“…In the absence of the reaction mixture, electronic metal−support interactions occur, which are expected to oxidize metallic copper. 42,43 Previous studies have also shown that at low loadings (1 wt % Cu), no metallic copper is present on the surface, even during CO treatment. 43 We therefore attribute the observed Cu 2p 3/2 photoemission to Cu + and/or Cu 2+ , which is underlined by our UV−vis results discussed next, which allow changes to be detected when switching between different gas environments.…”

“…45 In addition, a strong dependence of the state of copper on the gas phase at 180 °C was observed for 20 wt % Cu/CeO 2 , that is, mainly Cu 0 was detected during CO exposure and Cu + in the subsequent exposure to an inert gas. 42 At low loadings, for example, 1 wt % Cu/CeO 2 , the catalyst behaves differently, as rather Cu + is observed under a CO atmosphere, which is then further oxidized to Cu 2+ on switching to He, 43 indicative of electronic metal−support interactions.…”

Selective Formose Reaction under Microwave Irradiation

“…Production of organic compounds, which is not based on fossil resources, should be developed to realize sustainable societies. In particular, C1 chemistry, utilizing one-carbon compounds (e.g., carbon dioxide, formic acid, formaldehyde, and methanol) as starting materials, has been of increasing importance [2][3][4][5][6][7] . Formaldehyde has the molecular formula, CH 2 O, and thus can be oligomerized to form sugars (monosaccharides) because the general molecular formula of sugars is (CH 2 O) n .…”