Co K-edge XAS study on a new cobalt-doped-SiO2 pillared clay

New Co-doped-SiO2-sol pillared montmorillonite has been synthesized by inte rlayer hydrolysis and condensation of tetraethylorthosilicate (TEOS) in the presence of Co2+ ion using an organic template. The Co K-edge XANES and EX AFS analyses for the CoO-SiO2-PILC (before and after calcination) and for t he references such as CoO and Co(OH)(2) were performed in order to obtain e lectronic and local structural information of cobalt species, which may act as a catalytic active site for the selective reduction of NOx, hydrodesulf urization, and Fischer-Tropsch reaction. According to the XANES spectra, th e divalent cobalt ion is stabilized in an octahedral symmetry. The EXAFS re sult shows a significant change in local symmetry around cobalt ion upon ca lcination. The EXAFS fitting result before calcination shows that the cobal t species is in the form of hydroxide, with a small number of (Co-Co) pairs compared to the bulk Co(OH)(2). After calcining at 550 degreesC, the first nearest neighbours were fitted to six oxygen atoms with two different dist ances, and the second and the third neighbours were fitted to two Si and on e Co atoms. It is, therefore, reasonable to suggest a structure model, wher e the cobalt species on the SiO2 sol exists as a nano cluster of Co(OH)(2) before calcination but transforms to a nanosized cobalt oxide covalently bo und to the surface of SiO2 pillar after calcination.