Behaviour of copper–zirconium nasicon-type phosphate, CuIZr2(PO4)3, in the decomposition of isopropyl alcohol

Abstract

The phosphate catalyst Cu^IZr₂(PO₄)₃ has been studied for the decomposition of isopropyl alcohol. Catalytic activity was observed to correspond mainly to dehydrogenation features, (the formation of acetone). This phenomenon has been related tentatively to the migration of Cu^I ions towards the surface and to their reduction to metallic Cu under catalytic reaction conditions. This occurred without a change in the crystallographic structure with the replacement of Cu^I ions by protons. Evidence for this was provided by: (i) XRD peaks corresponding to (111) and (110) metallic Cu diffractions; (ii) UV–visible spectroscopy with the appearance of a conduction band at 575 nm and of hydroxyl group combination and acetone bands at 1380 and 2220 nm, respectively; (ii) the appearance of hydroxyl bands at 3450, 1280, 825 and 520 cm^–1 in the IR spectra and of protons detected by NMR; (iv) XPS analysis; and (v) SEM analysis, which showed the presence of 30 nm metallic Cu particles after catalytic reaction. Evidence was also seen that the formation of particles of Cu metal was reversible upon reoxidation at 240 °C, resulting in the formation of the Cu^IZr(PO₄)₃ starting material.