Structure of the Clean and Oxygen-Covered Cu(100) Surface at Room Temperature in the Presence of Methanol Vapor in the 10–200 mTorr Pressure Range

Abstract

Using ambient pressure X-ray photoelectron spectroscopy (APXPS) and high pressure scanning tunneling microscopy (HPSTM), we show that in equilibrium with 0.01-0.2 Torr of methanol vapor, at room temperature, the Cu(100) surface is covered with methoxy species forming a c(2 × 2) overlayer structure. In contrast, no methoxy is formed if the surface is saturated with an ordered oxygen layer, even when the methanol pressure is 0.2 Torr. At oxygen coverages below saturation, methanol dissociates and reacts with the atomic oxygen, producing methoxy and formate on the surface, and formaldehyde that desorbs to the gas phase. Unlike the case of pure carbon monoxide and carbon dioxide, methanol does not induce the restructuring of the Cu(100) surface. These results provide insight into catalytic anhydrous production of aldehydes.

High-Pressure Scanning Tunneling Microscopy

“…Methanol on Cu(100): Unlike the case of CO and CO 2 , no clustering of the Cu(100) surface was observed in the presence of methanol vapor. 79 HPSTM images taken in the presence of 0.01-0.2 Torr CH 3 OH at room temperature show a (√2×√2)R45° adlayer structure (Figure 20), which is due to a methoxy saturated surface, as shown by APXPS. 79 Sum frequency generation studies in Ref.…”

“…79 HPSTM images taken in the presence of 0.01-0.2 Torr CH 3 OH at room temperature show a (√2×√2)R45° adlayer structure (Figure 20), which is due to a methoxy saturated surface, as shown by APXPS. 79 Sum frequency generation studies in Ref. 80 also suggests polycrystalline Cu foils to be covered with methoxy in the presence of methanol vapor.…”

Recent Progress with In Situ Characterization of Interfacial Structures under a Solid–Gas Atmosphere by HP-STM and AP-XPS

“…As mentioned in previous literature, reconstruction appears on the Cu(100) surface under O 2 , CO, and CO 2 pressure [64,65,66]. Methanol is incapable of inducing reconstruction on the Cu(100) surface, according to studies of Eren et al In their other work, they conducted experiments where structural changes of clean and oxygen-covered Cu(100) surfaces under methanol vapor in the 10−200 mTorr pressure range at RT were studied, in light of HP-STM and AP-XPS [69]. As discussed previously, a small amount of atomic oxygen and OH groups are easily adsorbed on the surface of Cu(100), thus introducing the dark spots (depressions in STM contrast) in Figure 7a.…”

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.…”