Cu/SiO2 and Cu/SiO2-TiO2 catalysts. II. Identification of the active sites in the polymerization of 2,6-dimethylphenol in the presence of molecular oxygen

8% Cu/SiO2 and Cu/SiO2-TiO2 catalysts, prepared by the chemisorption hydrolysis method and characterised in the preceding paper (Boccuzzi et al., 1999, J. Catal., 184, 316-326) have been tested in the oxidative coupling of 2,6-dimethylphenol, a well-known copper catalysed reaction in the homogeneous phase. All of them proved to be active after reduction of the copper oxide initially present giving similar to 75% of PPE and <4% DPQ. Although they lost similar to 30% of the metal during the first run, they appeared to be reusable and more active during the second run. From HRTEM and FTIR characterisation before and after the polymerisation reaction, it can be deduced that three-dimensional copper particles are preferentially leached under the reaction conditions, while electron deficient two-dimensional metallic particles can be responsible for the catalytic activity.