| There are two goals in this study, one is to identify the potential poisons for SCR catalysts, the other is to develop new catalysts with better performance with the understanding the mechanism of the catalyst deactivation and poisoning.; The comprehensive study of the effects of poisons on SCR reaction shows that the catalyst reactivity is directly related to the basicity of the poison; Qualitatively, the results can be summarized as follows: for vanadia-based catalyst, strong poison-alkali metal oxides; weak poisons-oxides of alkaline earths, arsenic, lead, phosphorus and chlorides of strong alkaline metals. SO{dollar}sb2{dollar} is a promoter due to its acidity. HCl, although acidic, react with both MH{dollar}sb3{dollar}, (forming NH{dollar}sb4{dollar}Cl) and {dollar}rm Vsb2Osb5{dollar} (forming VCl{dollar}sb2{dollar} and VCl{dollar}sb3{dollar}) and consequently strongly deactivate the SCR reaction. Poisoning mechanism study by EHMO calculation and IR showed that the decreases in the Bronsted acidity by the addition of alkaline metals, and the order of the decrease follows the order of the basicity of the alkali metal. SO{dollar}sb2,{dollar} in contrast, increases the Bronsted acidity. Furthermore, dehydroxylation of the catalyst by heat treatment eliminate its activity, which is restored rapidly by exposure to water vapor. These results indicate that the Bronsted acid sites are the active centers for the reaction. Alkali metals poison the catalyst by decreasing and destroying its Bronsted acidity.; The roles of WO{dollar}sb3{dollar} in the commercial SCR catalyst {dollar}rm WOsb3{dollar}-{dollar}rm Vsb2Osb5/TiOsb2{dollar} also were studied. The catalysts were characterized by TPR, ammonia chemisorption and proton MAS NMR measurements. The following effects were observed: (1) It increases the activity and widens the temperature window for SCR by creating more Bronsted acid site. (2) It significantly increases the poison resistance to both alkali metal oxides and arsenic oxide. (3) It reduces NH{dollar}sb3{dollar} (as well as SO{dollar}sb2{dollar}) oxidation. |
