Synthesis, characterization and catalytic performance of Mg and Co substituted mesoporous aluminophosphates

Hexagonal mesoporous pure AlPO, MgAPO and CoAPO were synthesized at room temperature using cetyltrimethylammonium bromide as the structure-directing template. These materials were extensively characterized by low-angle XRD, TGA, N-2 adsorption, AAS, SEM, Al-27 and P-31 MAS-NMR, UV-Vis DRS and DRIFT (pyridine adsorption). XRD and N-2 adsorption studies clearly indicated that the porous structural integrities were retained even after calcination at 500 degreesC. The UV-Vis DRS spectroscopic studies demonstrated that incorporation of Co2+ is mostly isolated and substitutes predominantly for four co-ordinated aluminium species. Al-27 and P-31 MAS-NMR spectra revealed that Al and P are present in both tetrahedral and octahedral coordination. Isomorphic substitution of Mg and Co into the framework of AlPO creates Bronsted and Lewis acid sites, which is evidently proved by DRIFT (pyridine adsorption) experiments. tert-Butylation of in-cresol with tert-butyl alcohol was studied as a model reaction to evaluate their catalytic activity at temperatures between 175 and 325 degreesC. The major product is 2-tert-butyl-5-methyl phenol in addition to di-tert-butyl ether as minor product. The influence of various parameters such as temperature, reactant feed ratio, WHSV, time on stream and acidity on conversion and product selectivity was examined. The salient results are discussed in this manuscript. (C) 2004 Elsevier Inc. All rights reserved.