X-RAY-ABSORPTION SPECTROSCOPIC STUDY AT THE COBALT K-EDGE ON THE CALCINATION AND REDUCTION OF THE MICROPOROUS COBALT SILICOALUMINOPHOSPHATECATALYST COSAPO-34

The local environments about the cobalt atoms in as-synthesised, calci ned and hydrogen-reduced CoSAPO-34 have been studied by X-ray absorpti on spectroscopy. Calcination of the as-synthesised material and reduct ion in hydrogen of the product of calcination were carried out at 450 degrees C and for 6 h, respectively. The results show that cobalt is s ited as Co-II in the framework and that calcining CoSAPO-34 with 4.4% Co leads to two-thirds of the Co-II content being oxidised to Co-III t hereby lending support to the view that the material is a redox cataly st. Reducing the calcined material with hydrogen leads to a material c ontaining only Co-II. Taken together, the pre-edge, XANES and EXAFS re gions indicate that one-third of the original tetrahedrally coordinate d divalent cobalt in the as-synthesised product is maintained in the c alcined and reduced products with the remaining cobalt being in the fo rm of trivalent hexacoordinated and divalent hexacoordinated cobalt, r espectively.