Synthesis of stable Cu-supported pillared clays for wet tyrosol oxidation with H2O2

Abstract

In the present paper the synthesis of stable Cu-containing pillared clays catalysts (Cu-PILCs) is described. These catalysts were prepared by the solid-state reaction of Al-pillared clay with copper nitrate. The resultant materials were then treated with an oxalic acid solution in order to improve the dispersion of metal species on the alumina pillars. Characterization studies were performed by use of X-ray diffraction, nitrogen adsorption at 77K, chemical analysis, temperature-programmed reduction (H2-TPR) and transmission electron microscopy (TEM). The texture of the copper catalysts showed a high specific surface area and microporosity (197m2g−1 and 0.081cm3g−1 respectively for the catalyst Cu5.6Al-PILC), with high loading of copper (up to 4.72Cuwt%). TPRprofiles of catalysts show the presence of isolated copper species with high interaction with the alumina pillars.The properties of copper-based catalysts have been studied in the wet hydrogen peroxide oxidation of an aqueous solution of tyrosol, a molecule which constitutes more than half of the light fraction of the olive mill wastewater. The reaction was conducted in batch and flow reactors. Performance of catalysts remained quite excellent; total removal of tyrosol with high TOC abatement (around 65%) was obtained after 2h reaction. Furthermore, the Cu5.6Al-PILC(t) catalyst showed very high stability and performance in the flow reactor: 90% of tyrosol conversion and 78% of TOC removal are obtained in 192h on stream, without the detection of any change in the activity.