t-Butylation of phenol over mesoporous aluminophosphate and heteropolyacid supported aluminophosphate molecular sieves

Mesoporous aluminophosphate (AIPO) has been synthesized hydrothermally using cetyltrimethylammonium bromide (CTAB) as structure-directing agent in the presence of tetramethylammonium hydroxide (TMAOH) at room temperature. Phosphotungstic acid, H3PW12O40 (PW) was supported on the synthesized mesoporous AIPO at various loadings viz., 10, 20 and 40 wt.% to yield PW/AIPOs and characterized by XRD, TGA and FIF-IR. XRD patterns confirm that HPA retains the Keggin structure on the AIP0 surface and forms finely dispersed heteropoly acid (HPA) species. HPA crystal phase was not developed even at HPA loading as high as 40 wt.%. Catalytic activities of both parent AIP0 and HPA loaded AIPOs were studied by carrying out t-butylation of phenol with tert-butanol in vapour phase in the temperature range 190-250degreesC. The products obtained were o-tert-butyl phenol (o-t-BP), p-tert-butyl phenol (p-t-BP) and tert-butylphenyl ether (t-BPE) with high selectivity towards p-t-BP. The effects of feed ratio and WHSV towards conversion of phenol were studied and finally the time on stream studies were also carried out to compare the activities of the catalysts. PW/AIPO catalysts were found to yield higher conversion than parent AIPO due to the increase in Bronsted acid sites. Hence, PW/AIPO compositions are promising catalysts exclusively for acid type conversion of large organic molecules. (C) 2004 Elsevier B.V. All rights reserved.