Effects of commercial HFAU structural parameters over m-cresol transformation

The transformation of m-cresol was studied on a series of commercial HFAU z eolites (Si/Al = 3.9-100) at 653 K, and reactant partial pressure of 0.1 ba r. Whatever the catalyst samples the m-cresol was transformed into isomeris ation products (p- and o-cresol) and disproportionation products (phenol an d xylenols). The catalyst pore volume distribution was investigated by nitr ogen adsorption at 77 K, it was found that the micropores decreases, while meso and ultramicropores increase with decreasing N-FAL, as a result of the partial collapse of the micropore structure during dealumination procedure . The acidity was investigated by IR in the OH stretching vibrations (3800- 3400 cm(-1)) and by adsorption/desorption of pyridine followed by IR. For t his series of catalysts it was found, that both the Bronsted and the Lewis acid site concentrations grow with the number of framework aluminium atoms per unit cell. The nature and amount of extraframework aluminium species va ry from one sample to another and are strongly determined by the sample tre atment history. A portion of the extraframework aluminium species is of cat ionic nature capable of synergetic interaction with nearby Bronsted acid si tes, producing stronger sites, which are responsible for the 3600 and 3525 cm(-1) bands in the IR spectra. This is the case of the less dealuminated s amples (N-FAL = 34.9-39.2), consequently, the more active. The highly dealu minated samples (N-FAL = 1.9-4), contrary to what is commonly observed, has a weak Bronsted acidity, and therefore, lower activity, due to inhomogeneo us dealumination that leaves adjacent OH groups. The initial rates of isome risation reaction and p-cresol formation are higher than of disproportionat ion and o-cresol formation. The selectivity ratios IID and plo increased wi th increasing framework aluminium atoms. The stronger acid sites, of the le ss dealuminated samples, are capable of retaining the diphenylmethane inter mediate of disproportionation, transforming it to coke precursors, instead of to phenol and xylenol, as is the case for the weak acid sires of the mor e dealuminated samples. A close relationship between o-cresol formation and the disproportionation was observed, this could be associated to a possibl e bimolecular path to o-cresol formation via transalkylation of m-cresol wi th xylenol. (C) 2001 Elsevier Science B.V. All rights reserved.