An X-ray absorption spectroscopic study on the local environment of copper in CuAPO-5

Abstract

A copper-containing AlPO4-5 was synthesised using copper(II) oxide as the copper source and tetraethylammonium hydroxide as the template. The local environment about copper in the as-synthesised, calcined and hydrogen-reduced materials has been studied using XANES and EXAFS. The results for the as-synthesised product show that copper is sited within the AlPO4-5 framework and that its local environment is a tetragonally distorted Cu(O)6 octahedron in which the axial bonds are possibly to hydroxy groups. On calcining at 550 °C the environment changes to a non-tetragonally distorted octahedron for which the coordination to the framework is increased by two long bonds to framework oxygens. Copper(II) in CuAPO-5 is reduced by 5% H2 in He to copper particles of dimensions >40 Å. The catalytic properties of two CuAPO-5 samples (derived from copper(II) oxide and, for comparison, from copper(II) acetate) in the selective catalytic reduction of NO in the presence of NH3 and O2 have been investigated, showing maximum conversions of 27% at 440 °C and 53% at 340 °C, respectively.