Thermodynamic and structural study of methanol thin films adsorbed on MgO(100)

Semi-ionic Model for Metal Oxides and Their Interfaces with Organic Molecules

“…Elevated pressures do not change the coverage in the pressure range calculated. The sharp increase of coverage at low pressure has been observed by Trabelsi et al who reported the surface would be covered with a monolayer of methanol molecules at 2-8 Pa at 300 K. 44 However, this result is significantly different from that reported based on spectroscopic measurements on single crystals in which the full coverage does not occur until 8000 Pa. 40 This may be the result of the different experimental conditions and substrates used. Although the surface structures were not explicitly discussed in the references, it is likely the surfaces are not the same.…”

“…As a classical model system, methanol adsorption on the MgO surface has been studied by several research groups using various experimental methods. [40][41][42][43][44] Three types of species have been identified on the MgO surfaces: methanol physisorbed to the substrate, methanol "chemisorbed" to the substrate (Bush, ref 7). Characteristic fractional coordinates are listed for low-symmetry oxides.…”

“…43 It is generally accepted that the bond dissociations only occur on defect-rich sites. 43,45 Using volumetric adsorption isotherms and neutron diffraction spectra, Trabelsi et al 44 suggested two layers of methanol placed on the MgO (100) surface and a subdivision of the two layers at lower temperature. Despite the great interest in this system and ample experimental data reported in the literature, theoretical approaches have been limited to quantum mechanics calculations of small cluster models.…”

“…This is in contrast with deductions made based on the experimental work. 40,42,44 From the thermodynamic point of view, the oxygen atom in MgO is more polarized than that in the methanol; consequently, it is a (100) surfaces at room temperature (300 K). The calculations were performed on defect-free or modified surfaces; the experimental curves were measured on single-crystal surface.…”

A combined periodic DFT and QM/MM approach to understand the radical mechanism of the catalytic production of methanol from glycerol

“…Campbell and co-workers have compiled a review of the experimentally measured heats of adsorption for small molecules on the surfaces of a range of oxides. 44 The heat of adsorption of methanol to MgO(100) has been measured using equilibrium isotherms 45 giving Hads = -72 kJ mol -1 while temperature programmed desorption measurements 44 have been used to estimate Hads in the range 83.7 to 90.5 kJ mol -1 , depending on surface coverage, with the higher value from the lowest coverages. Table 2 shows that all the DFT methods underestimate the experimental values except for the periodic PBEsol+D3 models which give a value of Eads = -93 kJ mol -1 , which is close to the low coverage end of the experimental estimates.…”