Methanol Decomposition on Copper Surfaces under Ambient Conditions: Mechanism, Surface Kinetics, and Structure Sensitivity

Abstract

Here, we study the adsorption of methanol vapor under ambient pressure and temperature conditions on low-index Cu surfaces using surface-sensitive infrared (IR) and X-ray spectroscopy techniques. The first step of methanol decomposition, i.e., breaking of the O−H bond to form surface-bound methoxy, readily occurs under ambient conditions. Time-lapse IR spectra clearly indicate a gradually decreasing methoxy coverage, which does not obey wellestablished kinetic models. We rationalize the initial temperature-independent, high, nonequilibrium coverage of methoxy by a H-bonded methanol assembly in the precursor state. A temperature-dependent equilibrium coverage is achieved as the excess methoxy is eliminated gradually via further dehydrogenation to CO that desorbs to the gas phase. The kinetics of this process displays a significant structure sensitivity with considerably faster kinetics on the Cu(110) surface compared to Cu(111) and Cu(100) surfaces.

Conversion of CO2 to Methanol and Ethanol on Pt/CeOx/TiO2(110): Enabling Role of Water in C–C Bond Formation

“…The major surface species are adsorbed CO 3 /HCOO (290 eV), , CH 3 O (287 eV), − and CH x (284.5 eV) , groups. These species have already been detected in previous studies of CO 2 hydrogenation or methanol decomposition using XPS in combination with other surface science techniques. − The coverages of these C-containing groups on the Pt/CeO x /TiO 2 (110) catalyst were not large (<0.35 ML), being frequently small (<0.1 ML), see Figure b.…”

Hydrogen Exchange through Hydrogen Bonding between Methanol and Water in the Adsorbed State on Cu(111)

“…The PM-IRRAS experiments were performed in a dedicated UHV system which is described in detail in our previous works. ,, The base pressures in the preparation and measurement chambers were 2–5 × 10 –10 mbar and ∼1 × 10 –10 mbar, respectively. To clean the Cu(111) single crystal, 2–3 cycles of Ar + sputtering (5 × 10 –6 mbar, 1 kV, 20–30 min) and annealing (10 min at 773 K) were performed before each experiment.…”

“…This molecular adsorption step usually has a relatively short lifetime under realistic reaction conditions of temperature and pressure; however, it may determine the nature of the initial surface intermediates and thereby steer the following reaction pathway. A poignant illustration of the importance of molecular precursors in dissociative adsorption is methanol on Cu surfaces, which was discussed in one of our recent studies …”

“…A poignant illustration of the importance of molecular precursors in dissociative adsorption is methanol on Cu surfaces, which was discussed in one of our recent studies. 3 Two fundamental aspects of the interaction between methanol and water on metallic surfaces are the H-bonded structures and the hydrogen-atom transfer between the adsorbed molecules. Principally, the H-bonded structures and the adsorption geometry are derived from the energy balance between intermolecular interactions and the interaction with the surface.…”

“…A poignant illustration of the importance of molecular precursors in dissociative adsorption is methanol on Cu surfaces, which was discussed in one of our recent studies. 3 …”