Characterisation of copper catalysts and activity for the oxidation of phenol aqueous solutions

Several copper oxide catalysts supported on gamma-alumina were prepared under different conditions and characterised using techniques such as TPR, XRD, mass spectra, C-13 NMR, BET areas and SEM. The activation energies of reduction of the catalysts and the unsupported CuO were calculated using theoretical methods to study the interaction between copper oxide and gamma-alumina. A series of phase changes were also detected during the reaction process by XRD. At the same time, an aqueous solution of 5 g/1 in phenol was oxidized using air as oxidant and a continuous reactor under trickle in periods of eight days. All the catalysts were highly active and preferentially selected CO2 during the phenol oxidation reaction, The trickle bed reactor was clearly seen to inhibit the formation of polymeric products All the catalysts have different plateaus of phenol conversion. The first plateau has an approximate conversion of 80% and the increase in the calcination temperature decreases its lifetime. Free copper oxide seems to be responsible for this first plateau activity. For the active species of the second plateau, which shows an approximate conversion of 40%, we propose a new crystalline copper-oxalate (moolooite) phase produced during the reaction process, and a 'surface spinel' produced during the calcination process. (C) 1998 Elsevier Science B.V.