Study Of Supported OMS-2and α-MnO₂Catalytic Activity

Volatile organic compounds (VOCs) are the main source of atmosphericpollutants. BTEX is the representative gas of VOCs. Development of removal BTEXtechnology will have important significance for eliminating VOCs. Currently, themost effective elimination of VOCs method is deep catalytic oxidation, which canfully converted the VOCs to non-polluting CO2and H2O. This method showed goodcatalytic performance in removal VOCs, especially in the amulticomponent catalyticoxidation, low concentrations of VOCs. The supported noble metal catalyst’sperformance in the catalytic oxidation of the polluting gases is considered to be themost effective method in VOCs catalyst oxidation. Therefore, the research for theperformance of supported noble metal catalysts and explore catalytic mechanism, hasa very important practical significance. CO is a common atmospheric pollutant,mainly due to incomplete combustion of carbonaceous material. The catalyticoxidation of CO in the catalysis research foundation topics for CO study helps tofurther explore the catalytic mechanism. The catalytic oxidation of CO, also make animportant contribution to eliminate atmospheric pollution gas. In order to furtherstudy and discussion noble metal catalytic performance, the following studyconcluded that based on the experimental results.Au/OMS-2and Pt/OMS-2catalysts were prepared by pre-incorporation (QI),typical wet impregnation (IM) and deposition-precipitation (DP) methods. And-MnO2-supported gold catalysts were prepared by deposition-precipitation methodwith different conditions. The influences of prepared methods and conditions on thecatalytic activity of CO oxidation were studied. The samples were characterized byX-ray diffraction (XRD), Brunaner-Emmett-Teller (BET), N2adsorption-desorptionmeasurement, H2temperature-programmed reduction (TPR), Transmission electronmicroscope (TEM) and X-ray photoelectron spectroscopy (XPS). The following mainresearch results are obtained.(1) The results showed that compared with pre-incorporation and typical wetimpregnation methods, Au/OMS-2-DP prepared from deposition-precipitation (DP)method revealed the highest activity, due to the largest surface area and the smallestAu particle size. A study was conducted on the effects of different preparationconditions (i.e., precipitating agents, pH of solution, Au loading and calcinationstemperature) on the catalytic oxidation of CO over Au/OMS-2-DP. Results indicated that effects of precipitating agents on catalytic activity were obvious. The bestcatalytic activity was shown by the Au/OMS-2-DP catalyst prepared with KOH as aprecipitating agent, which could be explained in terms of the smallest Au particle size.A pH of9generated greater amounts of Au loading and smaller Au particles onOMS-2than other pH value. The sample calcined at300°C showed the highestactivity, which may be due to the sample’s calcined at200°C inability to decomposecompletely to metallic gold while the sample calcined at400°C had larger particles ofgold deposited on the support. It can be concluded from this study that Au/OMS-2-DPprepared from a gold solution with KOH as a precipitating agent, pH of9, Au loadingat5wt%, and a calcinations temperature of300°C provides the optimum catalyticactivity for CO oxidation, i.e.100%CO conversion at67oC.(2) Compared with typical wet impregnation method and pre-incorporation methods,Pt/OMS-2-DP, prepared from deposition-precipitation method, revealed higheractivity, due to the smaller particle size and the stronger interaction between Pt andOMS-2. The catalyst activity for catalytic oxidation of CO increased with an increaseof Pt loading and passed through a maximum in activity at3wt.%Pt. ThePt/OMS-2-DP(8) catalyst, prepared at pH=8solution, showed a significantimprovement catalytic activity as compared those prepared at other pH values. Thismay be due to interaction between OMS and Pt, which keep smaller particle size overOMS-2support.(3)-MnO2-supported gold catalysts (xAu/-MnO2,x=1.0-7.0wt%) were preparedby deposition-precipitation method using NaOH as precipitation agents andcharacterized by means of different characterization techniques such as X-raydiffraction (XRD), N2adsorption-desorption measurement, H2temperature-programmmed reduction (TPR), Transmission electron microscope (TEM) and X-rayphotoelectron spectroscopy (XPS). Catalytic activities of the materials were evaluatedfor the oxidation of benzene and toluene. The sizes of Au particle and-MnO2support were related with the Au loading over xAu/-MnO2samples and increasedwith Au loading. The result of XPS showed that the ratios of O2-/O2-, Mn4+/Mn3+andAu3+/Au0increase with adding of Au. It is shown that the loading of gold on-MnO2could significantly modify the catalytic activities. The catalytic performance ofxAu/-MnO2strongly depended upon the Au loading, among which3Au/-MnO2performed the best activity, T100=280oC and T100=250oC for the catalytic oxidationof benzene and toluene, respectively. The excellent performance of3Au/-MnO2was associated with the highly dispersed Au, good low-temperature reducibility, andsynergism at the interface ofAu and MnO2nanodomains.