| Volatile organic compounds (VOCs) have been widely applied in paint, pesticides, medicine and the organic chemical industry, etc. A majority of VOCs aromatic compounds have badly polluted the environment and affected human health. Therefore, the task of using the proper method to decompose aromatic compounds has been an important research in recent environmental treatments. It is considered an effective method to treat them with catalytic oxidation (also called catalytic combustion) that can directly oxidize o-xylene to CO2 and H2O. Here, deep catalytic oxidation of o-xylene was a model reaction and supported noble metal catalysts were investigated by using catalytic activity test, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area measurement, Scanning electron microscope (SEM), Energy dispersive spectrometer of X-ray (EDS), X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H2-TPR). Attention was particularly focused on the relation between the microstructure and catalytic activity of catalysts. The detailed contents were as follows:(1) A series of Pt/γ-Al2O3, Pd/γ-Al2O3 and Pt-Pd/γ-Al2O3 catalysts were prepared by impregnation method for deep catalytic oxidation of o-xylene. The loaded content and species of noble metals were investigated to affect the o-xylene conversion, the CO2 productivity, and CO2 selectivity. Simultaneously the difference in catalytic activity between supported single noble metal catalysts and double noble metals catalysts was compared. The results showed that Pd/γ-Al2O3 catalysts had a better catalytic activity than Pt/γ-Al2O3 catalysts for deep catalytic oxidation of o-xylene. The addition of Pt to the Pd/γ-Al2O3 catalyst could increase catalytic activity, which revealed that Pt had a stimulative effect on Pd/γ-Al2O3 catalyst. A complete o-xylene conversion and 97.3% CO2 productivity could be obtained at 185℃in the 0.08vol.% o-xylene flow over 0.5%Pt-2%Pd/γ-Al2O3 catalyst. In the 60-hour stability test, the Pt-Pd/γ-Al2O3 catalyst showed excellent catalytic performance.(2) Aluminum(Ⅲ) tri-isopropoxide and cerium(Ⅲ) nitrate were used as precursors. A series of CeAlO3 perovskite were prepared by sol-gel method and supported noble metal by impregnation method to get Pd/CeAlO3 catalysts. A different molar ratio of Ce/Al, a different species of noble metal or a different content of noble metal made a different effect on the activity of catalysts. Amongst the Pd/CeAlO3 catalyst, 2%Pd/CeAlO3-0.15 catalyst had the highest activity that a complete o-xylene conversion and 100% CO2 productivity could be obtained at 170℃in the 0.08vol.% o-xylene flow. The results of XRD, BET, SEM, EDS, XPS and H2-TPR showed that Pd and CeAlO3 had a cooperation effect to improve the activity of Pd/CeAlO3 catalyst.(3) Pd/Ce1-xLaxAlO3 catalysts were prepared by sol-gel method and impregnation method. It was investigated that different doped contents of La had different activity effects on the catalysts. The results showed that Pd/Ce1-xLaxAlO3 catalysts had a higher activity than Pd/CeAlO3 catalysts and 2%Pd/Ce0.8La0.2AlO3 catalyst was the best for T99=165℃,Yco2=100% at 165℃.In the series of Pt-Pd/Ce1-xLaxAlO3 catalysts, 0.5%Pt-2%Pd/Ce0.7La0.3AlO3 catalyst had the highest activity for T99=160℃,Yco2=98.7% at 160℃.The results of BET and XPS confirmed that Pt and La had a cooperation effect. The results of stability test showed Pt-Pd/Ce1-xLaxAlO3 catalysts had a stable catalytic activity. Therefore, Pt-Pd/Ce1-xLaxAlO3 catalysts can be used as an ideal catalyst for deep catalytic oxidation of o-xylene.
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