Fundamental studies of methanol synthesis from CO2 hydrogenation on Cu(111), Cu clusters, and Cu/ZnO(0001̄)

Abstract

A combination of experimental and theoretical methods were employed to investigate the synthesis of methanol via CO(2) hydrogenation (CO(2) + 3H(2)--> CH(3)OH + H(2)O) on Cu(111) and Cu nanoparticle surfaces. High pressure reactivity studies show that Cu nanoparticles supported on a ZnO(0001[combining macron]) single crystal exhibit a higher catalytic activity than the Cu(111) planar surface. Complementary density functional theory (DFT) calculations of methanol synthesis were also performed for a Cu(111) surface and unsupported Cu(29) nanoparticles, and the results support a higher activity for Cu nanoparticles. The DFT calculations show that methanol synthesis on Cu surfaces proceeds through a formate intermediate and the overall reaction rate is limited by both formate and dioxomethylene hydrogenation. Moreover, the superior activity of the nanoparticle is associated with its fluxionality and the presence of low-coordinated Cu sites, which stabilize the key intermediates, e.g. formate and dioxomethylene, and lower the barrier for the rate-limiting hydrogenation process. The reverse water-gas-shift (RWGS) reaction (CO(2) + H(2)--> CO + H(2)O) was experimentally observed to compete with methanol synthesis and was also considered in our DFT calculations. In agreement with experiment, the rate of the RWGS reaction on Cu nanoparticles is estimated to be approximately 2 orders of magnitude faster than methanol synthesis at T = 573 K. The experiments and calculations also indicate that CO produced by the fast RWGS reaction does not undergo subsequent hydrogenation to methanol, but instead simply accumulates as a product. Methanol production from CO hydrogenation via the RWGS pathway is hindered by the first hydrogenation of CO to formyl, which is not stable and prefers to dissociate into CO and H atoms on Cu. Our calculated results suggest that the methanol yield over Cu-based catalysts could be improved by adding dopants or promoters which are able to stabilize formyl species or facilitate the hydrogenation of formate and dioxomethylene.

Highly Active Au/δ-MoC and Cu/δ-MoC Catalysts for the Conversion of CO2: The Metal/C Ratio as a Key Factor Defining Activity, Selectivity, and Stability

“…[50][51][52] The largest rate of CO (or methanol) production per admetal atom was seen at coverages below 0.2 ML when many of the admetal particles are very small (< 1 nm) and two-dimensional. kcal/mol, than clean δ-MoC, 18 kcal/mol, or plain Cu(111), 37 22 kcal/mol. From the data in Figure 6, one can conclude that the Cu/δ-MoC system has unique properties for the reduction of CO 2 into CO.…”

“…From the data in Figure 6, one can conclude that the Cu/δ-MoC system has unique properties for the reduction of CO 2 into CO. The bare δ-MoC material presents worst activity than a model of a commercial Cu/ZnO catalysts, 37 but upon the addition of a small amount of Cu one obtains a remarkable catalyst for the reduction of CO 2 . In fact, Au/δ-MoC also exhibits a better activity than Cu/ZnO, although its performance is not as good as that of Cu/δ-MoC.…”

Production of methanol from CO2 electroreduction at Cu2O and Cu2O/ZnO-based electrodes in aqueous solution

“…Previous reports hypothesized that the stability of Cu-ZnO species may be a key factor for maintaining catalytic activity, since ZnO strengthen the Cu-CO -link, increasing the selectivity to alcohols, and stabilizing Cu in the hydrogenation reaction [21,38,41,42].…”

The bending machine: CO2activation and hydrogenation on δ-MoC(001) and β-Mo2C(001) surfaces

“…Product yields were analyzed by a gas chromatograph. 46,47 In our experiments data were collected at intervals of 15 min up to a total reaction time of 270 min. The amount of molecules (CO, CH 4 , or CH 3 OH) produced in the catalytic tests was normalized by the active area exposed by the sample and the total reaction time.…”