Catalytic oxidation of toluene with molecular oxygen overCr-substituted mesoporous materials

Abstract

The syntheses of thermallystable chromium-incorporating hexagonalmesoporousaluminophosphate and cubicCr-MCM-48 have been reported. Characterization of the catalysts was made using low angle XRD, N2adsorption, UV-VISDRS, thermalanalysis, ICP-AES and ESR. Mesoporous Cr-AlPO4and Cr-MCM-48 catalysts have been found to be active for the vapourphase oxidation of toluene with molecular oxygen. Mesoporous Cr-AlPO4is found to exhibit both acidic and redox propertiesand hence oxidation as well as dealkylation reactions are taking place in a concerted manner, whereas, the cubic silicateanalogue acts as a pure redox catalyst.© 2002 Elsevier Science B.V. All rights reserved.Keywords: Chromium; Aluminophosphates; Mesoporous materials; Partial oxidation1. IntroductionAluminophosphate materials, recently developed ascrystalline microporous materials are of potential usein catalysis [1]. Flanigen et al. [2] reported the incorpo-ration of various elements into the framework sites ofaluminophospahtes and the resulting systems are ac-tive for various catalytic transformations. However, thepore dimensions of these materials are not sufficient toaccommodate a broad spectrum of organic moleculesin their cavities. With the first discovery of M41S bythe Mobil researchers, a series of mesoporous ma-terials with pore dimensions greater than 20 Å havebeen synthesised using structure-directing templates.