| dc.description.abstract | VOCs exhausts have high volatile, high diffusivity and harmful for human body, therefore, how to reducing the amount of VOCs contamination is an important issue for environment protection. Catalytic oxidation is an effective way for treating the emissions of VOCs. Supported noble metal catalysts have been known as highly active catalysts for oxidation of hydrocarbons and have been preferentially used in commercial practices. The purpose of this study is to develop a low temperature reactivity and cost-effective metal catalyst for VOCs oxidation.
In this study, a series of Pd/CeO2、Pd/CuO-CeO2、Pd/MnOx-CeO2 catalysts with different metal additives were prepared by incipient-wetness impregnation method and co-precipitation method. These catalysts which compare different preparation method and add different metal or metal oxide to increase its activity were tested for total oxidation of toluene. Finally, we compare the properties and performance of these Pd based catalysts.
The samples were characterized by powder X-ray diffraction (XRD), N2-sorption, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy XPS and H2-TPR techniques. The catalysts were tested for total oxidation of toluene which the feed concentration was 8.564g/m3 (2085ppm) with GHSV=10,000h-1.
The XRD patterns showed the good crystalline but no palladium peaks were observed, which represent that the particle size of palladium was too small to detect (smaller than 4nm). The TEM and HRTEM images indicate that the average particle size of palladium was about 2-4 nm and disperse well on the support. The BET surface area showed that the catalysts in the same condition will change the surface area obviously by adding the metal additives and let more active sites combine with palladium. XPS spectra showed that when different metal additives add to the catalysts which can get more metallic palladium species and increase the activity of the toluene oxidation. For the reaction test, the supports synthesized by co-precipitation method were much more active than incipient-wetness impregnation method, which proved that the supports had the better interaction by using co-precipitation method.
A fixed bed continuous flow reactor was used to measure the activities of the toluene oxidation with Pd based catalysts. In all series catalysts, Pd/MnOx-CeO2 series showed the best activity especially added the Al and Zr which yielded 50% conversion at 96℃ and 134℃, and both completely oxidation of toluene at 190℃. In conclusion, adding appropriate additives to the Pd based catalysts could get the synergetic effect between the compositions which made the catalysts have better higher activity on toluene destruction. | en_US |