| Many environmental pollutions have been caused by NOx in the recent years. Due to the stricter standards for NOx emission, there is an urgent need for the development of NOx removal technology. Among these, the carbonaceous materials, due to their high specific surface area, good anti-deactivation and resource utilization, are getting more and more attentions. However, owing to the disordered structure and different pore sizes, the commercial activated carbon can not be utilized fully and the mechanism is still controversial. In order to solve these problems, ordered mesoporous carbon (OMC) may be a good option. Owing to the well-developed structural ordering and well-defined pore size distribution, ordered mesoporous carbon has been widely applied in catalysis, electrodes, and separations. In this dissertation, a series of OMCs with different pore sizes were synthesized and used in the NO removal. The adsorption mechanism of NO adsorption was investigated and the advantages of OMC to AC were analysized. In order to improve its NO adsorption capacity, metal component was introducted into OMC through EISA method. Based on the results, we chose the better components to test their NH3-SCR activity. Bimetallic catalysts were adopted to further improve the catalytic performance. At last, the adsorption kinetics was investigated to find the rate controlling step during the NO adsorption. The following are the main conclusion:At first,8kinds of OMCs with different pore sizes were synthesized through EISA method. It was found that the surface area, total pore volume and average pore size were all increased with the increment of F127. The N2adsorption isotherm showed that all the samples owned an ordered structure and small-angle XRD certified this conclusion, except that when the ratio of F127was too small. The reason may be that the organic component can not be composed regularly with too little F127. With the increase of F127the ordered mesoporous structure was obtained. TEM was used to observe their morphology. The results demonstrated that when the ratio of F127to resin was below6/5,the disorder structure was obtained. This was consistent with the small-angle XRD. In addition, when the ratio exceeded a certain value (14/5) the ordered structure was destroyed again. This may be due to that with the removal of F127during calcination the whole structure was sunk resulting from that there was no enough organic component.Then the self-made OMCs were used in NO adsorption. The results indicated that when the ratio of F127to resin was8/5, the NO adsorption capacity was the largest (16.35mg/g). The NO adsorption capacity of sample1, which did not own the ordered structure, was much lower than other ordered samples. With the increase of F127the NO adsorption capacity increased until the ratio reached8/5. Three desorption peaks were found in the desorption curves meaning that3adsortpion species. They were attributed to weakly adsorbed species, monodentate nitrito, and bridge monodentate nitrito. With the increase of pore size the latter two species increased significantly. The lower temperature and higher oxygen concentration were beneficial to the NO adsorption capacity. More NO concentration, more NO adsorption capacity. The NO adsorption mechanism on OMC was that NO molecule was adsorbed by C(O) groups which were formed by the combination of O2and active free site Cf. The monodentate nitrito (C-O-N=O) was the adsorption species when NO was adsorbed. In the desorption, the monodentate nitrito was decomposed into NO and C(O) groups. The C(O) group was not steady and continued to decompose into CO, CO2and Cf.In order to further improve the adsorption capacity9metal loaded OMCs were synthesized.The results indicated that with the addition of metal component the ordered mesoporous structure was observed.Wide-angle XRD and TEM tests demonstrated that the metal oxides were distributed uniformly on the OMC. We focused the study on cerium-containing OMC, and found that with the introduction of cerium the surface oxygen groups increased. The characterization test for the Ce-OMC and Ce-OMC ED (which was after exposure to the NO and O2) indicated that the introduction of cerium did not change the adsorption species and the role of cerium was that more adsorbed O atoms was provided through the transition of Ce3+ and Ce4+. As a result, more active free sites was transferred into C(O) groups and more NO molecules were adsorbed on the OMC.Based on the results of NO adsorption on M-OMCs, several M-OMCs were chosen to test NH3-SCR activity. The results showed that Cu-and Mn-containing OMCs had better catalytic performance. And with the increment of the metal content the NO conversion was greatly improved. To further improve the catalytic performance bimetallic loaded catalysts were adopted. Comparing with the monometallic catalysts the bimetallic catalyst owned stronger acid sites and oxidizing capacity and when the ratio of Cu to Mn equaled to1, optimum catalytic performance was obtained. The N2selectivity was inveatigated and all the catalysts exhibited more than90%selectivity. The stability test verified that the catalysts was steady during the test conditions. The synergetic effect was studied and the cycle of Mn3++Cu2+â†'Mn4++Cu+accelerated the recovery of active sites and thus the NO conversion was further improved.At last, the adsorption kinetics of NO on carbonaceous material was studied. The whole adsorption process was divided into three parts:external fluid film diffusion, intraparticle diffusion, and adsorption reaction. Four adsorption kinetic models were adopted to simulate the NO adsorption on AC, OMC and Ce-OMC. The results indicated that the external diffusion was not the rate controlling step. The NO adsorption capacity for OMC was much larger than that for AC. With the addition of cerium not only the adsorption capacity but the adsorption rate were increased. Oxygen played an important role in NO adsorption. When oxygen was absent, NO was mainly adsorbed in the form of physisorption. With the increase of oxygen the proportion of chemisorption increased. The intraparticle model divided the adsorption process into rapid adsorption, slow adsorption and equilibrium adsorption periods. The most difference between OMC and AC was the slow adsorption period, in which the adsorption rate was quicker and the adsorption time was longer for OMC. And thus the adsorption capacity in slow adsorption period for OMC was much larger than that for AC. This confirmed that OMC had advantages on mass transfer and internal surfaces. The rate controlling step was the intraparticle diffusion together with the adsorption reaction and pseudo-second-order model was the most suitable model for NO adsorption on OMC. |
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