Reduction of copper(II) with subsequent disproportionation of copper(I) during the hydrothermal syntheses of microporous silicoaluminium phosphates sapo-5 and -11

Abstract

The hydrothermal synthesis of SAPO-5 in the presence of copper(II) with weak and strong coordinating anions has been investigated. At temperatures above 190 °C, it is shown that copper(II) is reduced by the amine templates to copper(I) which, in the absence of coordinating anions (e.g. CI^–), disproportionates to metallic copper. This reduction/disproportionation in aqueous solutions by amines above this temperature is the first substantiated observation. Further, we observe that calcining the as-synthesised copper(II)-containing SAPO-5 produces copper(II) oxide mixed with SAPO-5, whereas for the corresponding SAPO-11 system copper(II) on extraframework positions has been previously reported. The result for the SAPO-5 system is consistent with the presence of metallic copper crystalities in the as-synthesised material. These results show that copper(II) cannot be incorporated into the SAPO-5 lattice to form CuSAPO-5 under the conditions prevailing in our synthesis.