Insight into the Balancing Effect of Active Cu Species for Hydrogenation of Carbon–Oxygen Bonds

Abstract

Hydrogenation of carbon–oxygen (C–O) bonds plays a significant role in organic synthesis. Cu-based catalysts have been extensively investigated because of their high selectivity in C–O hydrogenation. However, no consensus has been reached on the precise roles of Cu0 and Cu+ species for C–O hydrogenation reactions. Here we resolve this long-term dispute with a series of highly comparable Cu/SiO2 catalysts. All catalysts represent the full-range distribution of the Cu species and have similar general morphologies, which are detected and mutually corroborated by multiple characterizations. The results demonstrate that, when the accessible metallic Cu surface area is below a certain value, the catalytic activity of hydrogenation linearly increases with increasing Cu0 surface area, whereas it is primarily affected by the Cu+ surface area. Furthermore, the balancing effect of these two active Cu sites on enhancing the catalytic performance is demonstrated: the Cu+ sites adsorb the methoxy and acyl species, while the Cu0 facilitates the H2 decomposition. This insight into the precise roles of active species can lead to new possibilities in the rational design of catalysts for hydrogenation of C–O bonds.

Importance of the Initial Oxidation State of Copper for the Catalytic Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

“…Therefore, the ratio of Cu + and Cu 0 determines the conversion of DMO and the distribution of the products. Balancing the ratio of Cu + and Cu 0 is of great importance . If copper species are not reduced entirely, the active sites will be not abundant for the hydrogenation of DMO.…”

A Highly Porous Carbon Support Rich in Graphitic‐N Stabilizes Copper Nanocatalysts for Efficient Ethanol Dehydrogenation

“…X‐ray diffraction (XRD) patterns were obtained with a Panalytical X′pert Pro Super X‐ray diffractometer using CuK α radiation (40 kV, 40 mA, λ =0.15418 nm). H 2 –N 2 O titration was used to measure the copper dispersion and average particle size at 90 °C by using a procedure described in the literature . X‐ray photoelectron spectroscopy (XPS) data were obtained with a PHI 5000 Versaprobe spectrometer equipped with an AlK α X‐ray source.…”

Hydrogenation of biomass-derived compounds containing a carbonyl group over a copper-based nanocatalyst: Insight into the origin and influence of surface oxygen vacancies

“…Further, a broad and asymmetric Auger kinetic energy peak is observed from the Cu LMM XAES, indicative of the coexistence of Cu 0 and Cu + species in reduced CuMn-x samples (Fig. S8) [61], because of strong interaction between Cu species and supports [62]. This interaction, which originates from the homogeneous distributions of metal cations in the brucite-like layers of LDH precursors, can give rise to Cu + -O-M-like (M = Al or Mn) structures after reduction.…”