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Overall contribution of the catalyst structure and chemical composition to chemical or physical deactivation

The catalyst structure and the chemical composition have a significant influence on the NOx reduction capability, the SO2/SO3 conversion as well as on the resistance towards deactivation and the capability to oxidise elemental mercury.

A possible way to circumvent the loss of activity could be to increase the operating temperature of the catalyst. Another way to prolong the lifetime of the catalyst could be to increase the content of vanadium. Thereby the catalyst would be able to take up more potassium on an absolute level and remain active. The latter approach would only be possible for fuels with low sulfur contents since increasing vanadium content accelerates the undesired oxidation of SO2 to SO3 over the catalyst.

However, studies of this project show that simply increasing the operating temperature or the vanadium content in the catalyst cannot fully compensate the loss of catalyst activity. Increasing the temperature hardly increases the conversion of NO for the strongly poisoned catalysts and partly deactivated catalysts with high vanadium content become active for oxidizing NH3 to NO. For these reasons, it was decided to proceed the activities aiming at a change in chemical composition or in the physical structure of the catalysts not further. Changing a certain parameter included a large risk for manufacturers concerning the overall performance in a DeNOx reactor. The catalyst composition of standards types is very reliable and the performance in power plant operation can safely be guaranteed. This would otherwise not be the case and would require comprehensive demostration beyond the scope of this project.

Concerning the influence of the catalyst concerning the adsorbtion and oxidation or mercury sample catalysts with a specific composition of active components and surface composition have been tested. The results indicate that primarly elemental mercury is adsorbed on the sample catalyst with only one active component while the adsorption was insignificant on the standard catlyst mixture.

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Universität Stuttgart
Pfaffenwaldring 23
70569 Stuttgart
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