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

NASICON-type titanium and zirconium phosphates doped with rare-earth cations, A0.33M2(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.