The interaction of NO with Co2+/Co3+ redox Centres in CoAPOs Catalysts: FTIR and UV-Vis Investigations

The interaction of NO with Co2+/Co3+ redox sites in CoAPO-18 and CoAPO-5 catalysts was studied by means of FTIR and diffuse reflectance UV-Vis spectroscopy both at 298 and 85 K. Two families of Co2+ sites Were found in the CoAPO-18 structure. (A) ions in framework [Co2+(OH)P], associated with Bronsted acid sites which adsorb NO to produce dinitrosyls absorbing at 1903 and 1834 cm(-1) these dinitrosyl complexes are reactive, in that Co2+ is oxidized to Co3+ and N2O is formed. (B) Structural defects Co2+ (Lewis acid sites) which stabilize dinitrosyls absorbing at 1900 and 1813 cm(-1). The NO adsorption both on reduced and, more significantly, on oxidised CoAPO-18 also leads to the formation of NO2delta+ adsorbed species. It was found that the two kinds of dinitrosyl complexes have different reactivity in presence of oxygen. Both families of sites are also present in CoAPO-5 catalysts on which, however, the redox reaction upon NO adsorption does not occur significantly.