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

Abstract

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, 27Al and 31P 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 °C. The UV–Vis DRS spectroscopic studies demonstrated that incorporation of Co 2+ is mostly isolated and substitutes predominantly for four co-ordinated aluminium species. 27Al and 31P MAS–NMR spectra revealed that Al and P are present in both tetrahedral and octahedral co-ordination. 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 m-cresol with tert-butyl alcohol was studied as a model reaction to evaluate their catalytic activity at temperatures between 175 and 325 °C. 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.