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-synthesised, calcined and copper-incorporated SnAPO-5 have been studied using X-ray 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, with an oxygen multiplicity between five and six. X-Ray powder diffraction confirms that tin substitutes into the framework on positions that are close to the tetrahedral faces. Based on crystal chemical considerations it is suggested that tin is five-coordinate in a trigonal bipyramid with its second axial corner protruding into the extra-framework area. For the copper-incorporated material, Cu : SnAPO-5, EXAFS shows that the copper environment is tetragonally distorted octahedral. Powder diffraction confirms an extra-framework disordered square-planar copper-coordination connected to two framework oxygens by longer axial bonds. EXAFS results of calcined Cu : SnAPO-5 show that copper is sited near the tin sites in the framework.