Immobilization of dodecatungstophosphoric acid on dealuminated zeolite Y: a physicochemical study

12-Tungstophosphoric acid (PW12) has been supported on dealuminated zeolite Y. The catalysts were studied by XRD, DTA/DTG, IR, argon adsorption and MA S NMR spectroscopy. The structure of dealuminated faujasite is retained upo n contact with a very strong PW12 acid, which becomes thermally stabilized. Two types of Keggin anions exist at the surface: those strongly interactin g with the OH groups of the support, prevailing at low coverages, and those weakly interacting with the zeolite, prevailing at high coverages. Transfo rmations of m-xylene proceed along three pathways: isomerization, dispropor tionation and dealkylation, Pure zeolite shows high selectivity to isomeriz ation. Deposition of PW12 acid dramatically increases the selectivity of di sproportionation to toluene and trimethylbenzenes,which rises with the grow ing acid loading. (C) 2000 Elsevier Science B.V. All rights reserved.