Characterisation of CoIIand CoIIIin CoAPO molecular sieves

Abstract

CoAPO molecular sieves of the structure types 5, 11, 16 and 34 have been investigated by means of electron absorption spectroscopy, temperature-programmed reduction and infrared spectroscopy in combination with pyridine adsorption, the purpose being to determine the amounts of framework and non-framework cobalt and to study the properties of incorporated cobalt with respect to stability, redox behaviour and associated acidic properties. It has been shown that framework and non-framework cobalt species exhibit different spectroscopic properties and can be distinguished from each other. The framework cobalt acceptance and the stability of the different structures decrease in the order CoAPO₄-5 > CoAPO₄-11 > CoAPO₄-16 > CoAPO₄-34. In stable structures such as 5 and 11, framework cobalt can perform reversible redox reactions Co^II Co^III, which are accompanied by changes in the concentration of Brønsted and Lewis acid sites.