Study of Fe/Silicalite catalyst for the N2O oxidation of benzene to phenol

A set of Fe-silicalite samples of MFI structure have been prepared by the hydrothermal technique, followed by steaming and by further chemical treating of the solid. After characterisation by nitrogen adsorption/desorption, X-ray diffraction (XRD), scanning electron microscopy-electron probe micro analysis (SEM-EPMA), the samples have been tested as catalysts for the oxidation of benzene to phenol by N2O. The best performing catalyst has been studied also by temperature programmed desorption-mass spectrometry and temperature programmed reaction-mass spectrometry (TPD-TPR-MS), after pre-adsorption of both reactants and products. It was found that phenol forms when N2O is adsorbed first, followed by benzene. Almost no phenol formation was observed when adsorbing benzene before N2O. Furthermore, on this catalyst N2O decomposed since 50°C or less, forming gaseous N2 and adsorbed oxygen, which started to become available for the oxidation of benzene since 100–200°C. However, the so formed phenol remained adsorbed onto the catalyst. It desorbed within the 225–425°C temperature range, with a maximum around 300°C.