Abstract

A copper-containing AlPO₄-5 was synthesised using copper(II) acetate as the copper source. The local environments about copper in the as-synthesised and calcined materials have been studied using XANES and EXAFS. The results show that in the former copper is contained in Cu(O)₄ groupings which are linked to another Cu(O)₄ group at a Cu⋯Cu distance of 2.93 Å. On calcination the pairs separate with copper increasing its coordination to give a distorted Cu(O)₆ entity which is not incorporated into the AlPO₄-5 framework but linked to it via an (OAl/P–)₂ connectivity. This shows that copper(II) acetate is not a source for framework substitution of copper. For comparison Cu∶AlPO₄-5 was prepared in which copper was incorporated by the incipient wetness method. The EXAFS of the latter shows that copper is present in several environments, probably interacting with framework oxygen atoms.

The activities of these materials towards the selective catalytic reduction of NO_X to N₂ in the presence of hydrocarbons and oxygen was measured. CuAPO-5/CuAc₂ and Cu∶AlPO₄-5 both show low activity for this reaction (16.8% at 400 °C and 11.8% at 500 °C, respectively). The XANES show that autoreduction does not occur for these materials. This contrasts with CuZSM-5 which is an efficient catalyst for the same reaction and undergoes autoreduction.