Catalytic Activity of Materials Based on Complex Hafnium Phosphates with the NASICON Structure in Ethanol Conversion

Abstract

Materials with a NASICON structure having the composition (NH₄)_1−xH_xHf₂(PO₄)₃ (x = 0–1) have been obtained by hydrothermal synthesis followed by heat treatment and by ion exchange and characterized by X-ray powder diffraction, low-temperature nitrogen adsorption, and scanning electron microscopy. The catalytic activity of the materials in the conversion of ethanol is studied. All synthesized samples are shown to exhibit activity in the dehydration of ethanol and, to a small extent, the dehydrogenation of ethanol. At low temperatures, the conversion of ethanol predominantly results in the formation of diethyl ether and, at higher temperatures, the reaction predominantly affords ethylene. The selectivity in diethyl ether formation reaches 96% with 60% conversion at 360°C on the ion exchange–produced material of HHf₂(PO₄)₃ composition with a triclinic modification. At temperatures ≥450°C, the selective formation of ethylene is observed almost on all materials (~100%, with 100% conversion on NH₄Hf₂(PO₄)₃ with a rhombohedral modification at 450°C).