Deactivation Mechanism And Molecular Design On SCR Catalyst

The main pollutant in the atmosphere is NO_x. The most proven and effective removal technology of NO_x is selective catalytic reduction（SCR）. The principle of selective catalytic reduction（SCR） is the role of a catalyst by a suitable temperature, and the use of a reducing agent reduction the NO_x to N2 and H2 O. SCR catalyst is the core of denitration technology, however, in the industrial production SCR catalyst will be deactivated so that the denitration capability weakened. It is of great significance that to study the deactivation mechanism and design a highly effective catalyst. The model of the main catalyst V₂O₅ is established in this paper. The adsorption mechanism of V₂O₅ and NH₃, and the inactivating mechanism of alkali metals K and heavy metals Pb with the catalyst are studied. Finally, according to the molecular orbital theory of chemical reaction, the highly efficient catalyst are designed. Full results are as follows:（1） The research of the mechanism of NH₃ molecule adsorbed on the catalyst surface. This chapter focuses on the two adsorption models of NH₃ molecule with 2×2×1 V₂O₅（001） surface: The Top bit and Birdge bit of Lewis acid sites and the Br?nsted acid sites. The results show that, the chemical adsorption is occured between NH₃ and the Top bit and the Birdge bit of Lewis acid sites of the surface of V₂O₅（001）, in the adsorption process electron transfer from the N atom to adjacent H and the substrate. NH₃ molecule changes from neutral state to 0.896 and 0.931 positive charged, respectively, and be existence of covalently state NH₃; After the interaction of NH₃ molecule with the Br?nsted acid sites of 2×2×1 V₂O₅（001） surface, the V-O bond length becomes longer, the distance between H and NH₃ is close to the calculated bond lengths of NH₃ molecule; NH₃ molecule becomes positively charged cations after the adsorption. Further analysis of the density of states of two atomic adsorption models, indicating that O atom and H atom on the catalyst surface have strong chemical interaction with the NH₃ molecule.（2） The deactivation mechanism of alkali metal K, alkali chloride KCl and heavy metal Pb on the catalyst surface. The models are established, the deactivation mechanism of alkali metal K, alkali chloride KCl and heavy metal Pb on the catalyst surface are studied by using of density functional theory（DFT）. The adsorption energy, bond lengths before and Mulliken layout are calculated. Analysis showes that, K, KCl and Pb were form a strong chemical adsorption on the V₂O₅（001） surface, adsorption energies are-0.0985,-0.170,-0.136 Ha compared with-0.063 Ha adsorption of NH₃ are more negative, explain that the strong adsorption has occured. And will produce competitive adsorption with reducing gas NH₃, thus affecting the performance of the denitration of catalyst V₂O₅.（3） The design of the new type and high efficiency catalyst. Two types of six kinds of new type and high efficiency catalyst were desigened by frontier orbital theory, one type is the V atoms of the active site are substituted:W@V-V₂O₅, Mo@V-V₂O₅, Nb@V-V₂O₅; Another type is the ortho V atoms of the active site on the catalyst are substituted: W@o-V-V₂O₅, Mo@o-V-V₂O₅ and Nb@o-V-V₂O₅ catalyst. It can be speculated that the active site is substituted by W and Mo atoms and the ortho of active site of the catalyst V atom is replaced by Nb metal atom can be used as efficient catalyst.