CO2 adsorption and surface basicity evaluation of aluminophosphate oxynitride (AlPON) catalysts

Aluminophosphate oxynitrides (AlPON) are new catalysts obtained by nitridation of AlPO4 showing a high surface area and an enhanced surface basicity. In this article, surface basicity is evaluated by CO2 adsorption and related to the nitrogen content. CO2 simultaneously adsorbs linearly and as bidentate carbonate and bicarbonate species on AIPON surface. Particularly strong basic centers involving hydroxyls linked to Al cations and in the vicinity of terminal -PNH2 groups are identified. However, the influence of nitrogen content on surface basicity of AlPON is mostly through the change in the number of sites rather than on the modification of their strength. Activity results obtained for AIPON in base-catalyzed reactions are related with their capability of adsorbing CO2.