NASICON-type titanium and zirconium phosphates doped with rare-earth cations, A_0.33M₂(PO₄)₃ (M = Ti, Zr; A = Dy, Y, Yb), were synthesized using the sol–gel method and investigated as catalysts for ethanol dehydration at 300–400 °C. The catalysts were characterized via XRD, SEM, BET, and FTIR spectroscopy. The relationships between the catalyst composition, acidity and the dehydration activity were evaluated. Diethyl ether (DEE) formation is promoted by the presence of the zirconium phosphates (ZrP), while the presence of titanium phosphate (TiP) catalyzes the formation of both ethylene and diethyl ether (DEE). The application of Fourier-transform infrared (FTIR) spectroscopy to the analysis of adsorbed C₆H₆ has revealed the presence of hydroxyl groups exhibiting varying degrees of proton-donating mobility. This finding has enabled the correlation of the structure of the active sites with the process’s selectivity. The results underscore the key function of OH-group localization and framework geometry in the control of form-selective reactions.

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.