Frontier Molecular Orbital Based Analysis of Solid–Adsorbate Interactions over Group 13 Metal Oxide Surfaces

Adsorption is an
essential process that takes place in heterogeneous
catalysis. In the current study, solid–adsorbate interactions
occurring between a variety of small molecules and surfaces of group
13 metal oxides, including β-Ga2O3(100),
β-Ga2O3(001), θ-Al2O3(100), θ-Al2O3(001), θ-Al2O3(010), In2O3(110), and
In2O3(111), were investigated using density
functional theory calculations and a machine learning (ML)-based statistical
method. The adsorbates utilized for this purpose include CO, CO2, N2, NH3, H2O, acetonitrile,
acetone, acetamide, acetic acid, alkanes, alkenes, aromatic compounds,
alcohols, and amines. The results show that the adsorption energies
(Eads) of each metal oxide surface correlate
linearly with the highest occupied molecular orbital (HOMO) energies
of the adsorbates and not with energies of the lowest unoccupied molecular
orbital (LUMO) of the small molecules. Moreover, in these systems,
contributions to molecular adsorption are dominated by interactions
between the HOMOs of the adsorbates and the surface conduction band
of the metal oxides. Furthermore, the surface energy was found to
be an important parameter influencing Eads values of different metal oxides. Finally, the results of statistical
analysis using a ML approach confirmed that adsorbate HOMOs and surface
energy of metal oxides are the most influential factors governing
molecular adsorption, and also demonstrated that dipole moments of
adsorbates contribute to controlling to adsorption.