Glycerol adsorption and mechanism of dehydration to acrolein over TiO₂ surface: A density functional theory study

Glycerol as major by-product of biodiesel production cab be converted to high-value added materials such as acrolein. The details of this transformation mechanism is obscure using metal oxide catalysts. In this study, DFT calculations using the generalized gradient approximation with periodic boundary conditions was used to study the mechanism of dehydration of glycerol to acrolein on the (1 0 0) surface of anatase TiO₂. For this purpose, the (1 0 0) TiO₂ crystal face was built with a slab of Ti₂₄O₄₈. The various interaction of glycerol with the surface was surveyed, and energy barriers and reaction energies were employed to analyze the possible dehydration mechanisms. Three paths were proposed for dehydration of glycerol to acrolein that starts with adsorption through central hydroxyl group. According to the third path, TiO₂ surface shows the most activity in proton transfer reaction with 89.1 kcal/mol activation energy in comparison with path 1 and 2 is the appropriate path for the formation of acrolein. The rate-limiting step of this pathway is the adsorption of H2' and Oγ on the surface and simultaneous creation of a double bond between Cα and Cβ (G1h → G1o).