Characterization of intrazeolitic Fe 3+ prepared by chemical vapor deposition of [(C 5H 5)Fe(CO) 2] 2 inside NaY and FSM-16 zeolites and their catalytic activities towards phenol hydroxylation

Abstract

Iron-modified mesoporous and microporous zeolite materials, namely FSM-16 and NaY as well as dealuminated NaY (del-NaY), were prepared using cyclopentadienyl iron dicarbonyl diamer [(C 5H 5)Fe(CO) 2] 2 via a chemical vapor deposition (CVD) technique. XRD, FTIR, TG/DSC, N 2 adsorption and Mössbauer measurements were used to characterize the various materials. An isomorphous substitution of Fe 3+ into the framework of NaY zeolite was accomplished as determined from the Mössbauer results (IS≤0.3) as well as from the increase in the unit cell volume. As a further confirmation, some framework IR bands (780 and 574 cm −1) showed a shift towards lower frequencies upon iron incorporation along with the existence of a band at 686 cm −1 ascribed to SiOFe linkages. The latter band was emphasized on the basis of comparison of NaY before and after the CVD treatment with the precursor of the Fe complex. Two types of octahedral Fe 3+ components were revealed in FSM-16 and del-NaY samples specified as intrazeolitic iron oxide clusters and α-Fe 2O 3 species, which were localized on the external surfaces of zeolites and occupied small percentages (18–22%) compared with the former species. The surface area of the support NaY was preserved after the CVD treatment rather than FSM-16 that showed a reduction (24%). The catalytic activities of various samples for the liquid phase hydroxylation of phenol using H 2O 2 were found to be in the order: Fe/NaY>Fe/FSM-16>Fe/del-NaY. The higher activity of the Fe/NaY sample was attributed to the high dispersity of Fe ions that are located in framework positions and to the high crystallinity.