Roles of oxygen for methanol adsorption on polycrystalline copper surface revealed by sum frequency generation imaging microscopy

Abstract

The adsorption of atmospheric pressure methanol on the polycrystalline copper surface has been studied by a combination of sum frequency generation imaging microscopy (SFGIM) and temperature programmed desorption (TPD). Methoxy species can be generated by exposing the polycrystalline copper surface to methanol vapor at room temperature. SFGIM results demonstrate that oxygen promotes the surface adsorption of methanol and the increase in the amount of methoxy produced on copper surface. SFGIM orientation analysis suggests the methoxy monolayer is oriented closer to the surface normal with introduction of oxygen. Employing the image statistical analysis approach, the heterogeneities and conformation distribution of methoxy monolayers on copper surface with and without oxygen adsorption are compared. These results illustrate SFGIM indeed could provide more insight for understanding the heterogeneous metal/metal oxide surface in the molecular level.

High-Pressure Scanning Tunneling Microscopy

“…79 Sum frequency generation studies in Ref. 80 also suggests polycrystalline Cu foils to be covered with methoxy in the presence of methanol vapor. The absence of cluster formation could be understood by the small difference in the adsorption energy of methoxy on cluster edges compared to terraces, which is not sufficient to compensate the energy cost of detachment of Cu atoms to form clusters.…”

Sum frequency generation spectroscopy in heterogeneous model catalysis: a minireview of CO-related processes

“…PPP/SSP), or the ratio of CH 3-sym /CH 3-asym of the PPP spectrum, the orientation angle of adsorbates can be quantitatively determined. 32,33,46 In addition, SFG spectroscopy has also been widely applied for solid-liquid interfaces [9][10][11][12]70,71 and liquid-liquid interfaces, [72][73][74][75][76][77][78] related to electrochemistry, polymers, surfactants, biomolecules and others, and has been extended to SFG microscopy. 46,79,80…”

“…The SFG vibrational spectra provided insight into adsorption sites and adsorption configurations up to atmospheric pressure, for example the relative population of hollow/bride/on-top bonded CO or di-σ/π bonded ethylene/propylene. [41][42][43][44] Subsequently, SFG has also been employed to study the structure of adsorbates on polycrystalline foils, 45,46 thin films, 47 and supported nanoparticles (NPs of Pd, Pt, etc. ), 6,35 extending typical UHV surface science experiments to more realistic pressures and temperatures.…”

Identifying the catalyst chemical state and adsorbed species during methanol conversion on copper using ambient pressure X-ray spectroscopies

“…Surface-sensitive spectroscopies have been used to investigate the surface chemistry of the Cu catalyst both in ultra-high vacuum (UHV) and in the presence of gases, however almost of all of these studies focus on methanol adsorption and methanol oxidation. [4][5][6][7][8][9][10][11] The effects of water (either as a reactant, impurity in methanol, or as a by-product) are often not discussed. Concerning methanol adsorption and methanol oxidation, early work on Cu surfaces in UHV includes structural studies using X-ray absorption spectroscopy (XAS), scanning tunnelling microscopy (STM), and infrared reflection absorption spectroscopy (IRRAS), 4 as well as adsorbate identification with X-ray photoelectron spectroscopy (XPS) and other techniques.…”

“…5 XAS, XPS, and sum-frequency generation (SFG) were also used under ambient methanol pressures and reaction conditions. [6][7][8][9][10][11] Both in UHV and in the presence of methanol vapour, methoxy (OCH 3 ) is found to be the main reaction intermediate irrespective of whether single crystals, foils, powder catalysts, or supported nanoparticles are used. 2 It covers Cu surfaces at ambient pressures of methanol at room temperature (RT).…”