Structure-activity relationships in the production of olefins from alcohols and ethers: a first-principles theoretical study†
Olefin formation pathways on Lewis acid (LA) sites of Al2O3, Ga2O3 and In2O3 and gallium- and indium-doped alumina were investigated using Density Functional Theory (DFT) calculations. We considered two different olefin formation pathways, through alcohol dehydration and ether decomposition via both E1 and E2 type of elimination mechanisms. Both pathways evolve through a concerted E2 type of mechanism. Our results indicate that alumina is most active in alcohol dehydration reactions and the presence of dopants does not improve the catalytic activity. Correlations between the calculated energy barriers and the physicochemical properties of the oxides were identified and a dehydration model was constructed. The model accounts for surface acidity, base-site strength and the alcohol carbenium ion stability (CIS). We demonstrate a strong correlation between the ether decomposition and the alcohol dehydration barriers allowing us to extend the dehydration model predictions to ether decomposition chemistry.