Preparation Of Carbon-supported Nano-catalysts And Their Application In Catalytic Reduction Of NOx

Nitrogen oxides (NOx) discharged from power plants, waste incinerators, industrial boilers, engines, and automobiles can result in acid rain, photochemical smog, and ozone depletion. These adverse effects have aroused worldwide attention. Due to the increasing threat of NOx to the environment, many approaches have been investigated to control NOx emission. Selective catalytic reduction (SCR) technique has been proven to be one of the most effective methods for reducing NOx emissions. The keypoint for SCR technique is to develop novel and effective catalysts at low temperatures.In my thesis, we prepared a series of carbon supported catalysts through wet chemical methods and examined their catalytic performance for NOx removal. Great promotion effect was achieved upon introduction of carbon nanotubes to traditional catalyst V2Os-TiO2. To further improve catalytic reactivity of optimized catalyst, we dope a series of additional element such as Mn, Ce, Mo, Cr, Ni, Co to catalyst V2O5-TiO2-CNTs. Experimental results showed that CeOx can enhance SCR activity of catalysts greatly. We also synthesized three kind of catalysts in which carbon materials support CuOx and found a simple way to regenerate the deactivated catalysts.The introduction of carbon nanotubes to catalyst V2O5-TiO2 can promote its SCR performance greatly. The best reactivity of catalyst was achieved by doped 10% carbon nanotubes, the removal efficiency for NOx can reach up to 89%at 300℃.The specific surface, pore volume, acidity and reducibility of catalyst increased with introduction of carbon nanotubes. The high reducibility can enhance the oxidation efficiency of NO to NO2. The catalyst V2O5-TiO2-CNTs has a good resistence to SO2 and H2O.The combination of low-temperature active MnOx and high-temperature active V2O5 was accomplished by adding MnOx into V2O5/TiO2-CNT composites. A NOX removal efficiency of 99%was observed over V2O5-MnOx/TiO2-CNTs at 275℃under a GHSV of 36000 h"1. TOF results suggest a possible constructive interaction between V2O5 and MnOx for catalysts prepared by mechanical mixing. The possible separation of Mn and V with the assistance of CNTs and the increase of reducibility and acidic strength all contribute to the improvement of catalytic activity. Co, Ce. Cr, Mo, Ni were introduced to catalyst V2O5/T1O2-CNTS with sol-gel method and Ce was proved to be most effective to promote NH3-SCR activity. A large number of Ce3+contributes to the increase of chemisorbed oxygen, which favors the SCR activity. The aggregation of catalyst might be inhibited by CeOx thus result to the increase of specific surface. Moreover, the increase of surface acidity and reducibility both contribute to the extra NOx conversion upon addition of CeOx-The deactivation of catalyst VCeqTiC caused by SO2 depends on reaction temperatures and gas velocity strongly. And at least 2%of oxygen in exhaust gas is essential to keep high SCR activity.Cu-CNTs was prepared by wet impregnation method and a NOx removal efficiency of 67%was achieved at 250℃. which could be attributed to the good dispersion of CuOx, the existence of Cu+and strong acid sites on the catalysts" surface. Moreover, the regeneration of deactivated catalyst CuOx-CNTs caused by SO2 could be achieved by heating the catalyst in N2 at 300℃.