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.

The conversion and utilization of carbon dioxide is a critical challenge for the reduction of greenhouse gas pollution and in the production of high value chemicals in C1 chemistry. ZrO2/Cu­(111) is an inverse oxide/metal catalyst that displays high activity and stability for the hydrogenation of CO2 into methanol at 500–600 K. At elevated temperatures, ZrO2 grows on a CuO x /Cu­(111) substrate forming islands of 10–12 nm in size and an average height of ∼3 Å. Reaction with H2 leads to the removal of the copper oxide producing ZrO2/Cu­(111) surfaces which are very active for the binding and dissociation of CO2 into CO and C. After exposing ZrO2/Cu­(111) to moderate or elevated pressures of a CO2/H2 mixture at 300 K, atomic C and minor amounts of CH x O and CO x are deposited on the catalyst surface. The adsorbed CH x O and CO x disappear upon heating above 400 K. The catalytic tests for CO2 hydrogenation give CO as the main reaction product and CH4 and CH3OH as secondary products. The relative yields of methane and methanol change with time and track the amount of atomic C deposited on the active ZrO2/Cu­(111) surface. The formation of methane stops once the catalyst surface is saturated with C. Under steady-state conditions, ZrO2/Cu­(111) is a much better catalyst for methanol synthesis than ZnO/Cu(111). This trend reflects variations in the size of the oxide islands and in the strength of oxide-metal interactions. The use of an inverse oxide/metal configuration is an important synthetic tool when preparing active, selective, and stable catalysts for CO2 hydrogenation.

To activate methane at low or medium temperatures is a difficult task and a pre-requisite for the conversion of this light alkane into high value chemicals. Herein, we report the...

The dissociative adsorption of methanol was investigated on Cu(111) and ultrathin Cu 2 O films. We employed synchrotron-based Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS) and Scanning Tunneling Microscopy (STM) to study the dynamics of gas−solid interactions, and calculations based on Density Functional Theory (DFT) were used to examine the reaction path. C 1s XPS spectra revealed that methanol underwent dissociative adsorption on plain Cu(111) to form methoxy (CH 3 O), formaldehyde (H 2 CO), and formate (HCOO) at a pressure range of 0.5−10 mTorr, with these species remaining on the surface after evacuation. This was accompanied by the appearance of a low coverage (∼0.05 ML) of O ads in the O 1s which can be considered a highly active site for methanol activation. The high activity is apparent by a coverage of 0.8 ML of methoxy at room temperature. STM was unable to image these species at room temperature as they were highly mobile on metallic copper. In contrast, for CH 3 OH on Cu 2 O/Cu(111), STM showed clear hot spots for reaction and a complex array of adsorption structures. On the oxide substrate, there was decomposition of methanol to H 2 CO, CH 3 O, HCOO, and hydrocarbon species (CH x ) due to the subsequent interactions of methanol with lattice oxygen. Cu(111) remained entirely saturated with decomposition products under 10 mTorr of methanol (θ ≈ 0.97 ML), whereas the Cu 2 O overlayer was saturated at a much lower coverage (θ ≈ 0.30 ML). STM revealed rows and step edges of Cu 2 O decorated with decomposition products and metallic Cu islands ∼5 nm in size. The difference in activity between Cu(111) and Cu 2 O/ Cu(111) is attributed to the significant amount of O present on the oxide surface. Density Functional theory (DFT) calculations described the XPS measurements well, showing a likely methanol dissociation to *CH 3 O and therefore a surface reduction. More importantly, the DFT results revealed that it was the chemisorbed oxygen on Cu 2 O/Cu(111) which oxidized the dissociated *CH 3 O to *HCOO and eventually CO 2 , while the reaction only involving upper oxygen on the Cu 2 O hexagonal ring led to the formation of H 2 CO.

Inverse ZnO/Cu catalysts are key systems in the conversion of CO 2 , a common atmospheric pollutant, into methanol, a high-value chemical and fuel. The chemistry of methanol and methoxy groups over inverse ZnO/Cu 2 O/Cu(111) catalysts was investigated employing ambient pressure X-ray photoelectron spectroscopy (AP-XPS), scanning tunneling microscopy (STM), and calculations based on density functional theory (DFT). The results of AP-XPS show that the adsorption of methanol on the binary oxide substrate at 300 K leads to formation of *CH 3 O and *HCOO species with a minor amount of *CH x . Most of the methoxy groups disappeared from the surface after heating to 450 K, the onset temperature for the formation of methanol during the hydrogenation of CO 2 . The results of AP-XPS, STM, and DFT point to preferential adsorption of methoxy on the ZnO regions of the binary oxide. On the supported ZnO or on a ZnO−Cu 2 O interface, the breaking of the O−H bond in methanol is an exothermic process with a negligible (1−2 kcal/mol) or non-existent energy barrier depending on the size and shape of the ZnO islands. STM shows large changes in the morphology of ZnO/Cu 2 O/Cu(111) surfaces upon reaction with methanol. The produced *CH 3 O, *HCOO, and *CH x species are localized in groups of active sites that have a dynamic nature and their structure changes during the adsorption/desorption processes.