FTIR characterisation of Fe-silicalite catalysts for benzene oxidation to phenol by N2O

A series of Fe-silicalites with MFI structure, employed as catalysts in the title reaction, was investigated by FTIR analysis, using pyridine as the p robe molecule for acidity determination. The oxidation reaction was also mo nitored by FTIR spectroscopy on the best-performing catalyst. An optimal co ntent and distribution of extra-framework iron assures high selectivity, wh ile high acidity increases benzene conversion, but lowers the phenol yield. Benzene conversion to phenol occurs on N2O-pretreated Fe-silicalite cataly sts only and N2O does not adsorb as such on the catalyst, even at low tempe rature, but undergoes decomposition: this confirms the activating role of N 2O in the reaction mechanism. Under the experimental conditions adopted in reaction monitoring, the yield of adsorbed phenol is maximal around 550 K a nd the reaction is paralleled by the complete oxidation of benzene to CO2.