Modification of acid properties and catalytic properties of AlPO4 by hydrothermal pretreatment for methanol dehydration to dimethyl ether Original Research Article

An amorphous AlPO4 catalyst prepared by precipitation method was subjected to pretreatment with 10 mol% water vapor at 100–300 °C for 15 min prior to activity tests in the dehydration of methanol to dimethyl ether (DME). The catalysts pretreated at 200–300 °C exhibited higher methanol conversion than the non-treated catalyst while the one treated at a lower temperature of 100 °C showed lower activity. As revealed by FT-IR and FT-Raman results, there was an increase of lattice hydroxyls on the hydrothermally treated catalysts in the form of P-OH group (weak Brønsted acid sites). Amine titration using Hammett indicators confirmed the increase of both strength and number of acid sites on these catalysts. However, hydrothermal pretreatment at 100 °C may result in catalyst poisoning by weakly bonded water molecules instead so that lower catalyst activity was obtained. More than 99% selectivity to DME was achieved on both non-treated and hydrothermally treated AlPO4 catalysts in this study.