UV-VIS-NIR STUDIES OF FE(II)-A-ZEOLITE

U.v.-vis-n.i.r. spectroscopy was used to identify the consecutive form ation of hydrated octahedral, tetrahedral monoaquo, and trigonal bare Fe(II) species during the dehydration of Fe(II)-A zeolite. The amount of residual water was determined simultaneously using near-infrared wa ter vibration bands. The adsorption of NO probe molecules proved the a ccessibility of the surface trigonal iron sites. The resulting optical spectrum indicated the formation of a mononitrosyl [Fe(I)-NO+] comple x. Upon contact with O2 at 700 K, the ferrous ions of Fe(II)-A were ox idized to ferric species, consuming about one oxygen atom per two iron cations. Upon subsequent reduction with H-2, CH4, or CO at 600-700 K, most of the Fe cations were reduced back to surface trigonal Fe(II) s pecies, while a smaller fraction was converted to amorphous ferrous sp ecies. These amorphous oxidic species exhibited a higher redox activit y than that of the surface trigonal Fe cations.