Electron spin resonance study of the structural properties of copper–chromium oxide catalysts

Abstract

Copper–chromium catalysts with spinel structure and containing different amounts of copper are shown to have residual ferrimagnetic behaviour at room temperature. The small super-exchange interactions, sensitively characterized by octahedral Cr³⁺ e.s.r. linewidth and magnetic susceptibility determination, are drastically modified by redox treatment and variation of the Cu/Cr ratio. Comparison with ESCA results leads these modifications to be assigned to octahedral Cu⁺ concentration changes, which are quantitatively determined. Existence of such copper sites, even in the presence of isoprene, which is hydrogenated to mono-olefin, suggests that octahedral Cu⁺ ions play an important role in the selective hydrogenation catalysis.