Catalytic Ozonation Of Organics With Loaded Activated Carbon

In this study, copper and nickel loaded activated carbon catalysts (termed Cu/AC and Ni/AC) which were prepared under low temperature were characterized in various forms, followed by studies of application in the ozonation of phenol and oxalic acid. The effects of catalyst dosage, initial pH, concentration of tert-butanol and catalyst recycling in the catalytic ozonation were studied; degradation and reaction mechanism of heterogeneous catalytic ozonation of phenol and oxalic acid were further investigaed. The kinetics studies of O₃/Cu/AC, O₃/Ni/AC and the comparison study of two catalysts in catalytic ozonation were carried out by kinetic theory and experimental data.The XRD, SEM, BET and AAS characterization results of Cu/AC and Ni/AC showed that copper and nickel almost entirely in the form of rod-like structered CuO and NiO respectively loaded on the surface of Cu/AC and Ni/AC and both catalysts'surface morphologies were significantly changed. Compared with AC, the surface area, micropore surface area and pore volume of Cu/AC decreased by 50.7%, 62.9%, 62.4%; that of Ni/AC decreased by 47.9%, 60.6%, 60.7% and the average poresize of two catalysts slightly larger than that of AC.In O₃/Cu/AC and O₃/Ni/AC oxidation system, the removals of phenol and oxalic acid were positively correlated with catalyst dosage, which was mainly due to the increase of catalyst dosage leads to higher ozone decomposition efficiency and finally enhanced the oxidation capacity of system; the removals of phenol and oxalic acid under alkaline condition significantly higher than that of acid one, which is because the decompositon of ozone strongly influenced by the pH value of solution and ozone was mainly decomposed into HO^·in alkaline condition.The tert-butanol experiments showed that the processes of ozonation and O₃/AC mainly contained molecular ozone and activated carbon adsorption. The degradation of phenol and oxalic acid in O₃/Cu/AC and O₃/Ni/AC reactions follows the HO^·mechanism and catalysts promoted ozone decomposed into a certain amount of HO^·. The basic groups in activated carbon surface and the weak alkaline of metal oxides in Cu/AC and Ni/AC aroused the final pH values in catalytic ozonation slightly higher than that of ozonation. The leached Cu²⁺ and Ni²⁺ concentration in catalytic ozonation processes were very limited and the leaching rates were less than 0.5%, which indicating that Cu/AC and Ni/AC has high stability, easy to be recycled and the two catalytic reactions were heterogeneous catalytic ozonation.Kinetic studies and tert-butanol experiments showed that the rate constant of O₃/Cu/AC is smaller than that of O₃/Ni/AC and Ni/AC promoted ozone decomposed into more HO^·than Cu/AC. The catalytic effect difference of Ni/AC and Cu/AC is mainly because the unit molar metal conccentration in Ni/AC is 0.56mol·L^-1 larger than that of in Cu/AC and the BET of Ni/AC is 5% larger than Cu/AC. Therefore the reaction centers, exposure area and the collision of Ni/AC with ozone increased in O₃/Ni/AC system and the possibility and concentration of ozone decomposition into HO^·increased.