The dimer state of NO in micropores of Cu(OH)2-dispersed activated carbon fibres

Abstract

The magnetic susceptibility χ of Cu(OH)₂-dispersed activated carbon fibres [Cu(OH)₂–ACF] with and without adsorbed NO was measured in the temperature range 298–423 K in order to clarify the micropore filling of supercritical gaseous NO. Cu(OH)₂–ACF was characterized by N₂ adsorption and X-ray absorption spectroscopy (EXAFS and XANES). The micropores of Cu(OH)₂–ACF are very uniform and have larger pore volumes than those of non-modified ACF. EXAFS and XANES suggested ultrafine Cu(OH)₂ particles highly dispersed on the ACF. The χ value of Cu(OH)₂–ACF with 125–135 mg g^–1 NO was negative at 298 K and increased with temperature, while the χ value of Cu(OH)₂–ACF without NO was negative and independent of temperature; the negative χ is due to dimerization of NO in the micropores, and the increase of χ with temperature arises from the dissociation of the NO dimer and desorption of NO. The dissociation enthalpy of the dimer in the micropores is larger than that of the condensed phase at low temperature by 6–15 kJ mol^–1. The relationship between NO dimerization and the micropore filling of supercritical NO was discussed.