III International Conference

PP-I-16DIRECT OXIDATION OF BENZENE TO PHENOL BY NITROUS OXIDE:THE RADICAL NATURE OF ACTIVE OXYGEN INVOLVED IN THE REACTIONChernyavsky V.S., Pirutko L.V., Kharitonov A.S., Panov G.I.Boreskov Institute of Catalysis SB RAS, Novosibirsk, RussiaE-mail: cher@catalysis.ruCatalytic oxidation of benzene to phenol by nitrous oxide over Fe-MFI zeolites wasstudied in relation to the active oxygen species taking part in the oxidation. A lineardependence of the reaction rate on the concentration of independently identified active sitesgenerating O – radicals (α-sites) has been obtained within a broad range of values. Thedependence is interpreted as a convincing evidence of the O – involvement in the catalytic (notonly stoichiometric) oxidation of benzene to phenol.MFI zeolites of alumosilicate, borosilicate and titanosilicate composition were shown tobe inert in the benzene to phenol oxidation by nitrous oxide, but exhibit high activity andselectivity in this important reaction after the introduction of Fe [1, 2]. The active sites ofzeolite catalysts are extralattice complexes of bivalent iron2Fe α +(α-sites) stabilized in thezeolite matrix [3]. Upon N 2 O decomposition, these sites generate the so-called alpha-oxygenrepresented by monatomic oxygen radical Oα − , which is involved in highly selectiveoxidation of benzene to phenol.The catalytic role of α-sites was studied previously in many works. However, aquantitative correlation between zeolite activity and α-sites concentration (C α ) undercomparable conditions did not attract necessary attention. The present work considers thecatalytic properties of Fe-containing zeolite catalysts of various composition with α-sitesconcentration varying within two orders of magnitude. The obtained linear dependence of thereaction rate on C α (Fig. 1) reliably indicates that the reaction proceeds precisely on theα-sites.This conclusion is of particular importance in connection with a long discussion in theliterature on a possible role of O – radicals in selective oxidation catalysis over V and Mooxides. Reliable evidence of the catalytic role of O – obtained with zeolites may renew ageneral interest in the once suggested but not recognized radical oxygen idea in the oxidationover widely used metal oxide catalysts.36