Electron spin resonance and optical spectroscopic studies of Co-ZSM-5 with nitric oxide

The reaction of nitric oxide with ZSM-5 zeolite ion-exchanged by Co(II) (Co-ZSM-5) has been studied by electron spin resonance (ESR), Fourier transform infrared (FTIR) and diffuse reflectance ultraviolet-visible spectroscopy. When dehydrated Co-ZSM-5 reacts at room temperature with nitric oxide, the ESR spectrum of Co(II) atg = 5.5, which is only observable below 45 K, is greatly reduced and a new⁵⁹Co hyperfine octet forms at g_avg = 2.11. The overall Co(II) ESR intensity decreases by about 50% which suggests formation of some diamagnetic cobalt complex. Mononitrosyl cobalt complexes such as Co(I)-NO⁺ or less probably Co(III)-(NO)⁻ are suggested as possible precursors of a dintrosyl cobalt complex. The octet indicates hyperfine interaction with⁵⁹Co and is associated with a cobalt dinitrosyl complex. FTIR bands at 1813 and 1896 cm⁻¹ confirm a dinitrosyl species and a broad band from 1600–1800 cm⁻¹ is tentatively interpreted as a mononitrosyl species. The visible spectrum for dehydrated Co-ZSM-5 shows a tetrahedral Co(II) band from 500–700 nm with three components which disappears after NO adsorption at room temperature. We suggest that Co(0)-(NO)₂²⁺ forms after NO adsorption onto Co(II)-ZSM-5 zeolite on the basis of ESR and ultraviolet-visible spectroscopy.