Benzene Hydroxylation to Phenol Using Dinitrogen Monoxide
J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague
Selective oxidation of benzene to phenol with N2O was investigated on dehydrated H-ZSM-5, beta, mordenite, ferrierite and on hydrothermally treated H-ZSM-5 zeolites. It was found that three-dimensional zeoite structures of ZSM-5 and beta are best suited for the reaction, as they exhibit high activity and selectivity. In contrast, mordenite and ferrierite deactivate very fast because the reaction may proceed only in their main channels. The role of Bronsted and Lewis acid sites was investigated on H-(Al)ZSM-5 zeolite. No correlation was found between the oxidation activity and the Bronsted site concentration; only an apparent correlation of activity with the concentration of Lewis sites was obtained. The catalytic activity of H-(Al)ZSM-5 increased with increasing concentration of iron in the zeolite in the trace level range (30-1200 ppm). The catalytic activity of aluminosilicate zeolites increased after hydrothermal treatment. The complex extralattice iron sites, which cannot be removed by ion exchange using NaCl solution, were found to be active. Both the intensity of ESR signals of Fe(III) ions (g = 5.6 and 6.0; indicating Fe ions in distorted Td coordination in extralattice positions) and the intensity of FTIR bands of the perturbed lattice (reflecting the presence of Fe(II) ions in cationic positions) correlated semiquantitatively with the catalytic activity.
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