X-ray powder diffraction and EXAFS studies on SnAPO-5 and Cu : SnAPO-5

SnAPO-5 was synthesised and calcined at 800 degreesC. Copper was introduced into the calcined material by the incipient wetness method. The as-synthes ised, calcined and copper-incorporated SnAPO-5 have been studied using X-ra y powder diffraction and EXAFS. Rietveld refinements show that the overall microporous AlPO4-5 framework is unaffected by the incorporation of tin or copper. EXAFS shows that tin substitutes for aluminium and/or phosphorus, w ith an oxygen multiplicity between five and six. X-Ray powder diffraction c onfirms that tin substitutes into the framework on positions that are close to the tetrahedral faces. Based on crystal chemical considerations it is s uggested that tin is five-coordinate in a trigonal bipyramid with its secon d axial corner protruding into the extra-framework area. For the copper-inc orporated material, Cu : SnAPO-5, EXAFS shows that the copper environment i s tetragonally distorted octahedral. Powder diffraction confirms an extra-f ramework disordered square-planar copper-coordination connected to two fram ework oxygens by longer axial bonds. EXAFS results of calcined Cu : SnAPO-5 show that copper is sited near the tin sites in the framework.