• benzene oxidation;
  • catalysis;
  • ESR spectroscopy;
  • radicals;
  • spin trapping;
  • zeolites


The liquid-phase adsorption of benzene on copper-containing H,Na/ZSM-5 and H,Na/Y zeolites leads to the formation of various transient radical species, which may play a crucial role in the mechanism of the direct oxidation of benzene to phenol with molecular oxygen. The spin trap method at ambient temperature in combination with ESR spectroscopy is used to show the catalytic formation of large yields of radical intermediates on Cu,H/ZSM-5, but far less on Cu,Na/ZSM-5, and not at all in the absence of Cu. This requirement of both, the Cu redox activity and Brønsted acid centers, demonstrates that radical formation requires a bifunctional catalyst. It is conceivable but remains to be shown that the observed C6H5O radicals may react further to the desired phenol.