Electron paramagnetic resonance study of La cuprate-based catalysts for phenol oxidation

Abstract

A set of six La_{2 –x}Eu_xCuO_{4 +δ} samples, with x ranging from 0 to 1.33 have been analysed by EPR spectroscopy and X-ray diffractometry, to obtain information on their structure and on the change brought about by their use as catalysts for phenol oxidation with hydrogen peroxide. With increasing Eu content, a transformation of the orthorhombic structure of the La cuprate (x= 0) parent compound into two different T_La and T′_Eu tetragonal structures takes place, accompanied by a change of electrical conductivity and the appearance of particular features in the EPR spectrum. The latter was a most sensitive probe for monitoring the structural modification arising during the catalytic reaction, even during the very early stages when the XRD pattern does not yet show any significant change.