Development of Mossbauer Spectrometer System for Characterization of Catalysts and Its Application in Catalysis Chemistry

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A Mossbauer measurement system was developed for characterization of catalysts and their precursors. The system is composed of Mossbauer spectrometric modules and sample-mounting apparatus specially designed for measurement of unstable compounds and catalysts.The Mossbauer measurement system was applied to characterization of the precursors of silica-supported iron-rhodium catalysts. The Mossbauer spectra indicated that size and composition of iron-containing oxides on silica depended on preparation procedures including temperature of calcination.Phthalocyanineiron (II) synthesized in the zeolite supercage was also characterized by Mossbauer spectroscopy. Pyridine-adduct formation was suppressed by limitation of the residual space of the supercage containing phthalocyanineiron (II) molecule and interaction of pyridine with acid sites on the inner supercage. Mossbauer results demonstrate that the size of supercage and the population of acid sites influenced the reactivity of coordination compounds in the zeolite.Electronic and spin states of several iron (II) octahedral complexes with bidentate amines as ligands synthesized in zeolite supercage were also studied by Mossbauer spectroscopy. The Mossbauer parameters indicated that octahedral structure of some iron (II) complexes was distorted in the supercage due to the steric hindrance of the complex ions in the supercage of the zeolite. Mossbauer spectroscopy also indicated that the steric interaction influenced spincrossover of iron (II) complex with (2-aminomethyl) pyridine synthesized in the supercage.Iron (II) cyano-complexes on hydrotalcite was characterized also by Mossbauer spectroscopy. Preliminary results indicated that iron (II) was oxidized on the surface of hydrotalcite.The results obtained in the application studies demonstrate that Mossbauer characterization system using the devices developed in this research project is quite useful for designing new catalysts.