Active Cu⁰–Cu^σ+ Sites for the Hydrogenation of Carbon–Oxygen Bonds over Cu/CeO₂ Catalysts

Abstract

CeO2-supported copper species have been reported as an active catalyst for the hydrogenation of carbon–oxygen bonds (CO, CO2, furfural, esters, etc.). However, the identification of active sites remains challenging. Herein, we prepared a series of rod-shaped ceria-supported copper catalysts with different copper sizes (single-atom, 1.4 nm nanoclusters, 3.0 nm and 6.8 nm nanoparticles) and applied them for methyl acetate (MA) hydrogenation. The structure and chemical environment of copper species were detected, and the surface Cu0 and Cuσ+ species and defects (oxygen vacancy and M–[O x ]–Ce solid solution) were quantitatively measured. To identify the active sites for MA hydrogenation, we also prepared contrast samples with increased surface defects or with reduced Cu0–Cuσ+ species. It is demonstrated that the Cu0–Cuσ+ species rather than oxygen vacancies or M–[O x ]–Ce solid solution are the primary active sites for MA hydrogenation. From the results of in situ experiments and various chemisorption and density functional theory calculations, the Cu0–Cuσ+ interface located at the surface Cu deposits is evidenced to play the key role in enhancing the adsorption and activation of MA. The turnover frequency of Cu/CeO2 catalysts for MA hydrogenation is linearly increased with the increase of the Cu0–Cuσ+ interfacial perimeter. This insight into active sites for carbon–oxygen bond hydrogenation may provide guidance for high-performance catalyst design.

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

“…However, EDX verifies the presence of copper on the entire particles, for both large and small measuring areas (see Figure S1). Hence, the combined electron microscopy results point to the presence of highly dispersed copper on the surface of the ceria particles, in good agreement with the N 2 O–CO temperature-programmed desorption (TPD) results of a previous study on similarly prepared Cu/CeO 2 catalysts, which revealed a copper dispersion of 100% at a loading of 1.9 wt % …”

Efficient hydrodeoxygenation of guaiacol to phenol over Ru/Ti–SiO2 catalysts: the significance of defect-rich TiOx species

“…Conversion, selectivity, carbon balance and TOF were determined as follows:‡‡Moles of surface Ru were determined via CO adsorption. , §§Length of the Ru–TiO 2 perimeter was estimated using the following equation by assuming that Ru particles have a hemispherical shape: L = 2 S / d , in which S is the total surface area of Ru and d stands for the Ru particle size. 27 S and d were obtained from the CO adsorption results.…”

“…§Length of the Ru–TiO 2 perimeter was estimated using the following equation by assuming that Ru particles have a hemispherical shape: L = 2 S / d , in which S is the total surface area of Ru and d stands for the Ru particle size. 27 S and d were obtained from the CO adsorption results.…”

Ring-opening of furfuryl alcohol to pentanediol with extremely high selectivity over Cu/MFI catalysts with balanced Cu0–Cu+ and Brønsted acid sites

“…The synergistic effect exerted by Cu 0 and Cu + was considered to be the key to improving the catalytic performance. 19,45 The experimental results reveal that the PDO selectivity was closely related to the ratio of Cu 0 /(Cu 0 + Cu + ) and the content of Cu 0 . To get insights into the effect of the Cu 0 and Cu + sites present in the Cu/MFI catalyst on the conversion of FFA to PDO, the density functional theory (DFT) technique was used, as shown in Fig.…”

“…Among all reported non-noble metal catalysts, copperbased catalysts exhibit outstanding performance in the selective hydrogenation of CO/C-O bonds, are inactive towards cleavage of C-C bonds, and they have been intensely studied for the selective conversion of oxygenated compounds. [18][19][20][21] Chen reported an 85.8% conversion of furfuryl alcohol, with 48.6% selectivity of 1,2-PDO and 22.7% selectivity of 1,5-PDO, using highly dispersed Cu/Al 2 O 3 under 8.0 MPa of hydrogen pressure at 140 °C. It was considered that the close contact and interaction between the Cu and acidic alumina strengthened the performance.…”