The characteristics of iron-containing MFI type zeolites synthesized by different methods (direct synthesis, chemical vapor deposition, solid state reaction and ion exchange), in relation to their application for the one-step synthesis of benzene from phenol, were investigated by Mössbauer and NMR techniques. In the direct synthesis, the amount of iron incorporated in the zeolite framework depends on both its amount in the initial hydrogel and the TPABr template concentration. Part of these framework iron ions migrate to extra-framework position during catalytic tests and/or catalyst hydrothermal pretreatment forming active (Fe,Al)framework−O−(Fe,Al)extra-framework pair sites in which iron is in a distorted octahedral coordination. During long-term catalytic tests in benzene hydroxylation the iron ions migrate to more stable positions in the zeolite which is one of the cause of catalyst deactivation together with the formation of carbonaceous species and strongly chemisorbed phenol as detected by 13C-NMR. Introduction of iron by post-synthesis methods leads to a lower dispersion of iron and less stable species during the catalytic reaction.
One Step Benzene Oxidation to Phenol. Part I: Preparation and characterization of Fe-(Al) MFI type catalysts
PERATHONER, Siglinda;CENTI, Gabriele;
2002-01-01
Abstract
The characteristics of iron-containing MFI type zeolites synthesized by different methods (direct synthesis, chemical vapor deposition, solid state reaction and ion exchange), in relation to their application for the one-step synthesis of benzene from phenol, were investigated by Mössbauer and NMR techniques. In the direct synthesis, the amount of iron incorporated in the zeolite framework depends on both its amount in the initial hydrogel and the TPABr template concentration. Part of these framework iron ions migrate to extra-framework position during catalytic tests and/or catalyst hydrothermal pretreatment forming active (Fe,Al)framework−O−(Fe,Al)extra-framework pair sites in which iron is in a distorted octahedral coordination. During long-term catalytic tests in benzene hydroxylation the iron ions migrate to more stable positions in the zeolite which is one of the cause of catalyst deactivation together with the formation of carbonaceous species and strongly chemisorbed phenol as detected by 13C-NMR. Introduction of iron by post-synthesis methods leads to a lower dispersion of iron and less stable species during the catalytic reaction.Pubblicazioni consigliate
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