Nature of oxide-supported copper(II) ions and copper derived from copper(II) chloride

Abstract

Cu²⁺ derived from aqueous CuCl₂ solutions and supported upon silica and anatase, but not alumina, shows asymmetric e.s.r. peaks and an absence of X.p.s. shake-up satellite peaks. Consideration is given to whether this may be attributed in part to its higher dispersion and different constrained symmetry. Divalent copper is stabilised by these oxide supports but in two different forms: one highly dispersed (with properties detectable by X.p.s. and e.s.r.) and the other poorly dispersed [as Cu₂(OH)₃Cl-type species on alumina and CuCl₂ on silica and anatase] characterisable by X.r.d. In respect to its effect upon the X.p.s. and reduction (but not e.s.r.) properties of supported Cu²⁺ species, rutile is different from anatase, a phenomenon which may be of some value in optimising activity of heterogeneous catalysts. The results cast doubt upon X.p.s. diagnosis of divalent copper. Resistivity measurements for titania-supported copper after reduction at 700 K suggest that very little of the copper may have been intercalated into the anatase support, but that on rutile such an intercalation may have been significant. This may be relevant to SMSI effects, especially at even higher reduction temperatures.