Structural analysis of some alkaline-earth-metal–copper oxide catalysts for hydrocarbon oxidation or NO decomposition

Abstract

Some Ca–Cu–O, Sr–Cu–O and Ca–Sr–Cu–O defective perovskite-like mixtures have been prepared by the sol–gel technique and tested by means of a pulse reactor as possible catalysts for the title reactions. The characterisation of these preparations by several techniques, such as X-ray diffraction (XRD), scanning electron microscopy–electron probe microanalysis (SEM–EPMA), temperature-programmed desorption–temperature-programmed reaction–mass spectrometry (TPD–TPR–MS), electron paramagnetic resonance spectroscopy (EPR) and sorption–desorption of nitrogen, showed that the catalytic activity for both the reactions appears to be connected with the presence of a layer-like crystal structure approximating a two-dimensional antiferromagnet, stable within a sufficiently wide range of temperature. When oxygen, either added during the oxidation reaction or forming after the decomposition of NO, bridges together neighbouring Cu²⁺ ions not previously linked to oxygen, strongly interacting dipole systems form.