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 probe molecule for acidity determination. The oxidation reaction was also monitored by FTIR spectroscopy on the best-performing catalyst. An optimal content and distribution of extra-framework iron assures high selectivity, while high acidity increases benzene conversion, but lowers the phenol yield. Benzene conversion to phenol occurs on N2O-pretreated Fe-silicalite catalysts only and N2O does not adsorb as such on the catalyst, even at low temperature, but undergoes decomposition: this confirms the activating role of N2O in the reaction mechanism. Under the experimental conditions adopted in reaction monitoring, the yield of adsorbed phenol is maximal around 550 K and the reaction is paralleled by the complete oxidation of benzene to CO2.