Acid–base concerted mechanism in the dehydration of 1,4-butanediol over bixbyite rare earth oxide catalysts

•Adsorption structure of 1,4-butanediol on Er2O3 was elucidated by DFT calculation.•Interaction of 1,4-butanediol with Er2O3 was calculated by PIO theory.•Tridentate adsorption of 1,4-butanediol on Er2O3 accelerated the dehydration into 3-buten-1-ol.•Reaction mechanism in the dehydration of 1,4-butanediol over Er2O3 was elucidated.•The reaction proceeds via acid–base concerted mechanism over Er2O3.

Catalytic activity of rare earth oxides (REOs) in the vapor-phase dehydration of 1,4-butanediol to produce 3-buten-1-ol varies with lattice parameters of REOs. In order to clarify the adsorption structure and the reaction mechanism, adsorption energy of 1,4-butanediol on bixbyite REO, such as Sc2O3, Y2O3, Dy2O3, Ho2O3, and Er2O3, {2 2 2} surface was calculated with density functional theory (DFT), and paired interacting orbitals (PIO) calculation of the adsorption state between 1,4-butanediol and Er2O3 was executed. The DFT study elucidates that the catalytic activity is correlated with adsorption energy. The PIO study clarifies the interactions between the reactive atoms of 1,4-butanediol and Er2O3 surface: tridentate interactions between a position-2 hydrogen atom of diol and an oxygen anion on Er2O3 and between each OH group of diol and erbium cations on Er2O3, and an intramolecular repulsive interaction between the position-1 carbon atom and the oxygen atom of OH group are observed. These results suggest that the position-2 hydrogen atom is firstly abstracted by a basic oxygen anion and that the position-1 hydroxyl group is subsequently abstracted by an acidic erbium cation. Another OH group on position 4 plays an important role of anchoring the diol to the Er2O3 surface. Therefore, it is proved that the dehydration of 1,4-butanediol over REOs proceeds via acid–base concerted mechanism.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (154 K)Download as PowerPoint slide