Surface Design Of Iron-containing Zeolites And Its Catalytic Performance

Transition-metal-containing zeolites catalysts have received considerable attention due to their catalytic potential in the field of environmental and industrial catalysis research. The introduction of high dispersed metal-oxo units into the framework and extraframework of zeolites, the construction of transition metal compounds with well-defined component on the surface of zeolites, and the relationships between structure, activity and component of the modified zeolites were established via micro-structural and catalytic performance studies. These studies had great academic and applied significance for both designing the high efficient catalysts and revealing micro-essence of catalysis. In this paper, we studied on the reaction of ferrocene with HY and HZSM-5 by surface organometallic chemistry, and attempted to obtain cyclopentadiene iron species with well-defined structure and component anchored on their extraframework. Then iron-containing Y zeolite with single site iron-oxo units was prepared through subsequent treatment. We investigated the reaction of ferrocene with the hydroxyl of various zeolites by in situ FTIR spectrum under vaccum condition, such as HY, NaY, HZSM-5, MCM-41 The chemical composition, structure and property of the grafted sample were characterized in detail by in situ FTIR, ICP, XRD, TPD-MS and UV-Vis DRS. And the state and micro-structure of iron on the extraframework of HY zeolite were characterized by in situ IR probe, DRS and XAFS. The iron-grafted HY zeolite was used as catalyst for the catalytic oxidation of carbon monoxide. The results showed that: (1) Ferrocene ,at 423K ,could react with the acid hydroxyl group of the HY and HZSM-5 to form a new "half-sandwich"cyclopentadiene iron species CpHFe (OZ≡)₃(Z: Si or Al within the framework of zeolite ). This reaction did not occur to ferrocene adsorbed into NaY and MCM-41 under the same condition. Ferrocene was decomposed directly at elevated temperature. (2) The cyclopentadiene iron species CpHFe (OZ≡)3 grafted on the surface of HZSM-5 exhibited higher thermal-stability than that of HY under high vaccum or at inert atmosphere. The thermal-decomposed temperature of the former is at 523K,and the latter is at 423K. (3) The iron-containing Yzeolite, after treated at 773K under O2 atmosphere,which possessed high isolated Fe-O-Al units bonded to the zeolites. It exihibited higher catalytic activity for the oxidation of carbon monoxide than that of the Fe/Y sample prepared by the impregnated method. (4) The relations between the state and micro-structure of the active center of the iron-grafted HY sample and catalytic activity were examined by DRS, XAFS and in situ IR probe. We proposed the single site iron-oxo species located on the surface of the zeolite as catalytic active center. The innovation of this study as follow: We found firstly that ferrocene can react with the acid zeolites, and obtained the "half-sandwich"cyclopetadiene iron species CpHFe (OZ≡)3, which anchored into zeolite cavities. The chemical composition, structure and property of the grafted sample were characterized in detail by various physicochemical tools. The high dispersed iron-oxo units located on the extraframework of Y zeolite were prepared by the subsequent treatment, which possessed high catalytic activity for the oxidation of carbon monoxide.