Performance of Fe-BEA catalysts for the selective hydroxylation of benzene with N2O

Abstract

The catalytic performance and the formation of carbon in Fe-BEA and Fe-MFI catalysts prepared by three methods (hydrothermal synthesis, ion-exchange at room temperature with an iron-nitrate solution and ion-exchange at 80°C with an iron ammonium sulfate solution) are analyzed with the aim to develop catalysts having larger dimensions of the cavities with respect to the MFI structure (such as ZSM-5 and silicalite) and which could be applied in the selective hydroxylation of molecules having larger kinetic diameters than benzene. The results show that, apart from minor differences, Fe-BEA catalysts have comparable catalytic performances in selective benzene hydroxylation to phenol with respect to Fe-MFI catalysts. However, all the Fe-BEA samples show a higher formation of carbon than the corresponding Fe-MFI samples as well as the formation of carbon having a higher degree of condensation. This is connected to the larger cavities in the BEA framework, especially at the intersections of the channels, with respect to the MFI framework. Highly active samples were obtained by ion-exchange at 80°C with the iron ammonium sulfate solution. The phenol productivity in both Fe-MFI and Fe-BEA samples is about 60–70% higher than that of comparable samples prepared by hydrothermal synthesis.