Continuous Measurement Of Total Organic Carbon Employing Supercritical Water Oxidation

Volatile organic compounds (VOCs) are some of the most harmful air pollutants because they are acutely toxic toward the environment and humans. Among various available techniques, catalytic combustion is an effective and widely applied technology for the abatement of VOCs. In this present work, we prepared Cu-Mn-Ce mixed-oxide catalysts, their catalytic activities were evaluated in the catalytic combustion of toluene. The reaction mechanisms and structural features of these mixed-oxide catalysts were also discussed.A series of Cu, Mn, and Ce mixed oxides with different Cu/Mn/Ce ratios was prepared by citrate sol-gel method, and their catalytic activities were evaluated by combustion of toluene. The results show that the activity of Cu-Mn-Ce ternary mixed-oxide catalysts is higher than those of Cu-Mn and Cu-Ce mixed-oxide catalysts. With the partial substitution of Mn by Ce, the activity of Cu-Mn-Ce catalysts is promoted. Additionly, the Cu1Mn2Ce4catalyst appears to be superior for toluene catalytic combustion, which reaches99.0%conversion when the reaction proceeds at about220℃. This result is similar to those for conventional noble metal catalysts, such as Pd and Pt.In order to improve the thermal stability of the Cu-Mn-Ce mixed-oxide catalysts, the catalytic activities of Cu-Mn-Ce doped with La were also evaluated, which resulting in the significant improvement of catalytic activity and stability in toluene combustion.To gain deep insight into the catalytic properties of Cu-Mn-Ce mixed oxides, catalysts were characterized by XRD, BET, H2-TPR, and XPS analyses. Meanwhile, a new mechanism consisting of four elementary steps is schematized. The partial substitution of Mn by Ce in Cu-Mn catalyst induces a significant change in the structure of Cu-Mn mixed oxide catalyst. A new phase of ceria-based solid solution with fluorite structure forms, and excess Cu and Mn exist on the surface of ceria-based solid solution. The CeO2-based solid solution serves as the oxygen-supplying center with the function of transporting active oxygen, including surface and lattice oxygen. Cu-Mn mixed oxides are highly dispersed on the surface of CeO2as an active phase and can strongly activate organic molecules, thereby serving as the catalyst oxidation center. Then, an effective catalytic cycle consisting of adsorption dehydrogenation, oxidation, and regeneration is completed.