Influence of platinum on the performance of beta zeolite-based catalysts for xylenes production

M.C. RANGEL; S.T.F. GRECCO; D.R. DE CARVALHO; E.A. URQUIETA-GONZÁLEZ; J.M. GRAU; P. REYES; M. OPORTUS

Xylenes: Synthesis, characterisation and physicochemical properties

Nova Science Publishers

Lugar: New York; Año: 2013; p. 57 - 70

Xylenes are important raw materials with considerable application for chemicals and petrochemicals industry such as the production of synthetic fibers, plastics, resins and other products. The major sources of these compounds, naphtha reforming and gasoline pyrolysis, generate an appreciable amount of toluene and trimethylbenzene. The production of xylenes can be optimized by transalkylation of these compounds or by toluene disproportionation. The commercial process uses large pore zeolites which, however, deactivate with time mainly due to coke formation. In order to obtain new catalysts for these reactions, catalysts based on beta zeolite containing 0.5 and 1.0% platinum were synthesized and evaluated in toluene disproportionation. Zeolite-based materials were prepared by a two-step procedure and the metal was incorporated in the catalysts by wetness impregnation or by introducing platinum in the zeolite synthesis gel. The catalysts were characterized by differential thermal analysis, thermogravimetry, Fourier transformed infrared spectroscopy, X-ray diffraction, and adsorption/desorption of nitrogen and transmission electron microscopy. The activities of metallic and acidic sites were evaluated by cyclohexane dehydrogenation, a model reaction for both kinds of sites. All catalysts were more active than the commercial mordenite in toluene disproportionation, carried out at 470 ºC and 1 atm. Platinum decreased the activity but increased the xylene selectivity, especially p-xylenes. The most promising catalyst was prepared by incorporating platinum (0.5%) by impregnation, which produces the highest amount of xylenes, mainly p-xylenes and m-xylenes, high value chemicals.