Nitrogen Monoxide Adsorption and Contact Decomposition Properties of Co(II) Complexes

Abstract

We have carried out the feasibility study on the contact decomposition of NO by metal complexes such as metallotetraphenylporphyrins (MTPPs: M = Co (II), Cr (III), Zn (II), Ag (II), Ru (II) ) and Co (salen). Firstly, the NO adsorption properties of these metal complexes were evaluated by UV-vis and FT-IR spectroscopy. Among these complexes, both CoTPP and Co (salen) showed excellent NO adsorption ability. Two kinds of NO- species adsorbed on the center metal ion were observed for both CoTPP and Co (salen), and a new peak (1528 cm^-1) which was assigned to a bridging NO between two adjacent NO^- molecules appeared gradually for Co (salen) by the exposure to NO at around 1000 ppm. In the case of CoTPP, the bridging NO was observed by the exposure to NO of higher than 1 %.
Secondly, the contact decomposition properties of NO were investigated using CoTPP and Co (salen). These complexes were impregnated with porous glasses and employed as catalysts. Main decomposition species were N₂0 and N₂. The performance of the NO decomposition by Co (salen) was better than that of CoTPP. The maximum efficiency of NO decomposition at 190 °C by Co (salen) was 84% for inlet gas (NO: 300 ppm, O₂: 0.9%, in He). These results indicate that the NO contact decomposition is possible under O₂ coexistence condition without any reduction reagent.