Ethanol Dehydration Pathways on NASICON-Type A₀.₃₃M₂(PO₄)₃ (A=Dy, Y, Yb); M = Ti, Zr) catalysts: The Role of Hydroxyl Group Proton Mobility in Selectivity Control

The effects of NASICON-type phosphates composition on the dehydration of oxygen-containing molecules were probed in reactions of ethanol over double Ti- and Zr-phosphates with rare earth cations A0.33M2(PO4)3 (M – Ti4+, Zr4+; A – Dy3+, Y3+, Yb3+) at low temperatures (300 − 400℃). The catalysts were characterised via XRD, SEM, BET, and FTIR spectroscopy. Ethylene production was observed on Ti-phosphate, while the formation of diethyl ether (DEE) was observed on Zr-phosphate. The difference in the selectivity of ethanol dehydration is due to the presence of various types of hydroxyl groups characterised by different proton donor mobility depending on the composition of the Ti- and Zr-containing phosphates, which was determined by FTIR analysis of C6H6 adsorption. This work provides a strategy to design highly selective catalysts with framework structure for form-selective reactions with oxygenates considering the location of OH−groups as well as the pore size available for surface intermediates.