Nature and mode of addition of phosphate precursor in the synthesis of aluminum phosphate and its influence on methanol dehydration to dimethyl ether

Abstract

Four aluminum phosphate catalysts with Al/P = 1 were prepared by precipitation of mixture of aluminum nitrate and phosphate precursor (either phosphoric acid or diammonium hydrogen phosphate) with NH 3 and precipitation of aluminum nitrate with NH 3 followed by impregnation of phosphate precursor (either phosphoric acid or diammonium hydrogen phosphate). The catalysts were characterized, using different physico-chemical methods viz., BET-S.A., XRD, FT-IR, and NH 3-TPD. 27Al and 31P MAS NMR spectroscopy was used to characterize selected catalysts in order to find out the presence of Al and P environments. The catalytic conversion of methanol to dimethyl ether was conducted over these catalysts in a temperature range of 448–548 K at atmospheric pressure. AlPO 4 prepared by precipitating the mixture of aluminum nitrate and (NH 4) 2HPO 4 with aq. NH 3 generated more number of moderate acid sites and showed higher methanol dehydration activity with 100% selectivity to DME at 548 K.