Study On Selective Reduction Of NO_x By NH₃ Over Composite Catalysts

In view of the current research status of NH3-SCR of NOx,Co-Ce-TiOx composite metal oxide catalysts and red mud supported catalysts have been successfully prepared in this study,and the performance of these catalysts were tested.Meanwhile,the catalysts were characterized by SEM,BET,XRF,XRD,XPS,H2-TPR and in-situ DRIFTS.Based on the characterization,the structure of these catalysts have been found and the reaction mechanism of NH3-SCR of NOx has been proposed.Ce0.1-Ti0.9Ox,Co0.1-Ti0.9Ox and Co-Ce-TiOx were synthesized by hydrothermal method.The results showed that the catalytic activity,N2 selectivity and water-sulfur resistance of the catalysts were greatly improved after the introduction of Co and Ce.Co-Ce-TiOx catalyst with the molar ratio of Co:Ce:Ti=1:1:8 showed the highest performance.Over 90%NOx conversion was obtained between 250 and 450?.The characterization results showed that the addition of Ce could enhance the specific surface area and improve the pore structure of Co-Ce-TiOx,which is beneficial to the dispersion of active components on the catalyst surface.At the same time,the synergistic effect between Co and Ce could make the redox cycle occur in the form of Ce3++Co3+??Ce4++Co2+.The redox cycle facilitates the transfer of electrons between different components.The synergestic effect also leads to enhanced Bronsted(B)acid sites and lewis(L)acid sites,which contributes to the adsorption and activation of NH3.H2-TPR reulsts showed that the redox property of Co-Ce-TiOx catalyst was also improved compared with Co-TiOx and Ce-TiOx catalysts.The enhanced redox property and the acidity promotes the NH3-SCR of NOx.In order to reduce the cost of the catalyst,the waste residue(red mud)produced in the production of alumina was employed and a series of red mud supported Mn-Ce-TiOx catalysts were prepared.The results showed that the addition of Mn,Ce and Ti can greatly improve the DeNOx efficiency of the catalyst.5%Mn-2%Ce-10%TiOx/PTRM is the most active catalyst,over which the conversion rate of NOx is above 90%at 200?,and the active temperature window is between 200 and 450?.Moreover,this catalyst showed relatively high tolerance to water and SO2.The characterization results showed that the morphology of the PTRM was changed,and its surface particles became smaller and flaky.The doped Mn-Ce-Ti can interact with the substances in PTRM thus improving the pore structure and the specific surface area.At the same time,the crystallinity of catalyst is reduced,making Mn-Ce-Ti evenly dispersed on the surface of PTRM.This study shows that red mud has great potential as deNOx catalyst.