Synthesis, characterisation and catalytic evaluation of mesoporous AlPO supported phosphotungstic acid in the ethylation of ethylbenzene

Hexagonal mesoporous aluminophosphate (AlPO) was synthesised at room temperature using cetyltrimethylammonium bromide (CTAB) as the structure-directing agent. The mesoporosity of the synthesised material was confirmed from low angle XRD, TGA and nitrogen physisorption studies. Its textural properties were analysed with SEM and the framework vibrations by FT-IR. 27Al and 31P MAS NMR spectra revealed tetrahedral co-ordination of Al and P. The mesoporous AlPO was then impregnated with phosphotungstic acid, H3PW12O40 (PW), of various loadings viz., 10, 20 and 40 wt% of PW. The PW loaded AlPOs were characterised by XRD, FT-IR, BET, DRIFT and 31P MAS NMR techniques. XRD patterns reveal the presence of Keggin structure in 20 and 40 wt% PW/AlPO. Temperature programmed desorption of pyridine by DRIFT studies indicate modified acidity values due to transfer of protons to the support AlPO. The catalytic activity of the materials was examined in the vapour phase ethylation of ethylbenzene with diethyl carbonate at temperatures between 200 and 275 °C. 20 wt% PW/AlPO was found to be more active than 10 and 40 wt% PW/AlPO catalysts. Among the alkylated products, the most significant product is hexaethylbenzene, obtained only with 20 wt% PW/AlPO. The selectivity of p-diethylbenzene is higher than for other alkylated products. The time on stream study over 20 wt% PW/AlPO catalyst indicates similar activity for about 4 h of stream. The effect of feed ratio and WHSV on conversion and product selectivity was also examined and the results are discussed.