Quantum chemical study of the mechanism of the catalytic oxyethylation of ethylene glycol on phosphorus-doped titanium dioxide: The role of the surface phosphoryl and hydroxyl groups of the catalyst

DFT calculations of the oxyethylation pathways of monoethylene glycol (MEG) and diethylene glycol (DEG) were performed on a model fragment of phosphorus-doped titanium dioxide (anatase). It was shown that the surface hydroxyl group of titanium dioxide, whose proton initiates C-O bond cleavage in the ethylene oxide molecule, plays the key role in the activation of the molecule. At the same time, the phosphoryl group -P(OH)₂O activates the reactant molecule R (MEG, DEG, etc.) and carries out the synchronous proton transfer from R to the hydroxyl oxygen atom of titanium dioxide, thus restoring the catalyst structure and closing the catalytic cycle. This restructuring occurs synchronously in one step. The substitution of the catalyst hydroxyl groups by alkoxyl groups can influence oxyethylation occurring via the bimolecular nucleophilic substitution mechanism and can poison the catalyst in some cases.