Probing Cobalt Sites in CoAPO-11 via Spectroscopic and Activity Studies

Abstract

A systematic study undertaken for the oxidation state, coordination, stability of cobalt in CoAPO-11 structure by means of spectroscopic and catalytic activity, is presented. AlPO-11 containing Co(II) in the tetrahedral coordination was indicated by powder diffraction, electronic and EPR data. During calcination of Co(II) was partly converted to Co(III) and reverted back to Co(II) upon exposure to atmosphere. Apart from micropores, CoAPO-11 sample contains mesopores, which possibly arise from interparticle void space. The tetrahedral location of Co(II) was inferred from EPR data. The rectangular to spherical shapes of CoAPO-11 material was evident from electron micrographs. Activity studies revealed that o-cresol can selectively be converted to o-hydroxy benzoic acid. Moderate activity of CoAPO-11 along with spectroscopic analysis supports the fact that Co(II) is predominantly located in tetrahedral framework and do not convert to Co(III) effectively, as a consequence Co(II) are stable and do not display appreciable oxidative ability under mild reaction conditions.