Supercritical (Subcritical) Water Route For The Syntheses Of Composite Metal Oxides Toward Catalytic Oxidation Of Toluene

Catalytic combustion method has been considered as one of the most promising technology for the removal of volatile organic compounds (VOCs) due to its persisted high efficiency, low energy consumption and non secondary pollution, etc. The key to this technology is to choose an efficient, suitable synthetic method for the syntheses of reliable catalysts with high activity and stability. In this thesis, a novel, efficient and relatively "green" synthetic method, i.e. continuous hydrothermal flow synthesis (CHFS) route, was employed for the syntheses of Pd and Pt bimetallic supported cat-alysts and MnOx-CeO2 composite catalysts. The effects of unique crystallizing envi-ronment of supercritical water (sc-H2O) on the properties and toluene combustion ac-tivities of resulted catalysts were extensively explored.Firstly, we have synthesized a series of Pd/NiO catalysts by using the CHFS route and explored their catalytic activities in toluene combustion. It was noted that based on sc-H2O crystalizing environment, the one-step prepared Pd/NiO was shown with high surface area and redox potential as compared to that prepared via wetness impregnation route, which yielded the T100 (100% conversion of toluene) at ca. 273 C. With adding a reducing agent (formic acid) into sc-H2O reactor, the synthetic method was shown able to adjust the valence of Pd where more Pd(0) was obtained, which improved the activity of Pd/NiO catalyst with the T100 at ca.200 C. The modi-fication of Pt led to a formation of sc-Pd-Pt/NiO-R catalyst, which showed an even higher activity in toluene oxidation. The T100 was measured at only ca.170 C with the mineralization rate of 100% and did not show obvious activity decline after a long-term test at 170 C for 50 h.Secondly, we have synthesized a series of Pt/CeO2 catalysts by using the CHFS route and explored their catalytic activities in toluene combustion. It was noted that the unique crystalizing environment of sc-H2O had induced a strong metal-support interaction between Pt and CeO2, which yielded the T100 at ca.225℃ for the catalyst. With adding the reducing agent (formic acid) into sc-H2O reactor, the catalyst was obtained with more Pt0 with a promoted activity of T100 at ca.175℃. Further modi-fication of Pt and NiO onto the Pt/CeO2 catalyst had led an even higher activity in to-luene oxidation. The T100 was measured at only ca.150℃ with the mineralization rate of 100% and did not show obvious activity decline after a long-term test at 250 C for 50 h.Finally, we have synthesized a series of M-Ce-O catalysts (where M=Mn, Fe, Co, Ni) by using the CHFS route and explored their catalytic activities in toluene combustion. It was noted that the Mn doping had yielded the highest activity. The op-timized Mn/(Mn+Ce) molar ratio was measured at ca.0.20, which yielded the T100 for toluene oxidation at ca.240℃. Further modification of Mg had promoted the thermal stability and catalytic activity for the catalyst, which showed the Tjoo at ca.220℃ with the mineralization rate of 100% and did not show obvious activity decline after a long-term test at 220 C for 50 h.