Growth, Structure, and Catalytic Properties of ZnO_x Grown on CuO_x/Cu(111) Surfaces

Abstract

A catalyst with a ZnO/Cu configuration plays an important role in the synthesis of methanol from CO 2 hydrogenation. In this study, scanning tunneling microscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the growth mode of small coverages of ZnO x , θ oxi < 0.3 monolayer, on a Cu(111) substrate. Our results show that the modes of growth, size, and shape of the ZnO nanoparticles are strongly dependent on the Zn deposition temperature. In a set of experiments, Zn was deposited on Cu(111) or CuO x / Cu(111) surfaces at 300 K with subsequent exposure to O 2 at higher temperatures (400−550 K), which exhibited small particles of ZnO (<20 nm in size) on the surface. The deposition of Zn onto CuO x /Cu(111) at elevated temperatures (450−600 K) in an oxygen ambient produced large ZnO islands (300−650 nm in size), which were very rough and spread over several terraces of Cu(111). XPS/Auger spectra showed that all of the preparation conditions stated above led to the formation ZnO/CuO x /Cu(111) surfaces where the oxidation state of zinc was uniform. Catalytic tests showed that all these surfaces were active for the hydrogenation of CO 2 to methanol, but only the systems prepared at 600 K displayed long-term stability under reaction conditions.

Hydroxylation of ZnO/Cu(1 1 1) inverse catalysts under ambient water vapor and the water–gas shift reaction

“…Studies of scanning tunneling microscopy (STM) have been carried out examining the growth of ZnO nanoparticles on Cu(1 1 1) [12]. The growth mode, size, and shape of the ZnO nanoparticles were strongly dependent on the Zn deposition temperature [12].…”

“…Studies of scanning tunneling microscopy (STM) have been carried out examining the growth of ZnO nanoparticles on Cu(1 1 1) [12]. The growth mode, size, and shape of the ZnO nanoparticles were strongly dependent on the Zn deposition temperature [12]. In a set of experiments, Zn was vapor deposited on Cu(1 1 1) or CuO x /Cu(1 1 1) surfaces under an atmosphere of O 2 at the elevated temperatures typically used in catalytic processes for C1 conversion (550-600 K) [12,13].…”

Catalysts based on transition metals for applications in energy conversion

“…Contrary to Co3O4, the Zn LMM Auger electron spectra for both tested catalysts (figure 15d and 15e) demonstrate that ZnO support does not undergo any significant reduction process. 83,131 These observations suggest that Co 0 (ca. 778.1 or 778. mTorr of H2 to simulate reverse water-gas shift reaction conditions (Figure 16a-f).…”

“…This benchmark catalyst display an excellent performance for methanol synthesis under elevated pressures of CO2 and H2.. 72,83,84 It has been generally accepted that synergistic effects between ZnO and copper (Cu) nanoparticles play a crucial role to form the catalytic active phase in these systems. 72,83,85 In light of importance of this catalyst system for CO2 hydrogenation, special interest has been placed on optimizing its configuration for the conversion of CO2 into other valuable chemicals aside from methanol. However, despite the fact that Cu/ZnO/Al2O3 catalyst is selective towards CO at ambient pressure conditions, Cu can lead to low CO2 conversion.…”

“…This peak can be assigned to the presence of Zn 0 which indicates that ZnO support was reduced to some extent. 83,131 As shown in figure 16c and 16h, In order to further rationalize the structural behavior of Ni/ZnO catalysts, we investigated these materials using time-resolved X-ray diffraction (XRD). This in situ technique is another equally important powerful tool for studying the behavior of heterogeneous catalysts under reaction conditions.…”