OCR Text |
Show With this understanding of catalyst construction, the mechanisms of deactivation irrespective of the form the catalyst will be discussed. Activity Measurement and Degradation Initial catalyst activity is plotted in the attached curves (see Figure 1). These are commonly referred to as light-off curves. The light-off curve represents the percent (%) oxidation of a known VOC as it flows across a flXed amount of a specific catalyst at a given inlet temperature. After some period of operation this light-off curve may shift to the right (increasing temperature) indicating a loss of activity and a lowering of the effectiveness of the system. 100 75 t-------i • ...... ...... . . ..... ..... ~ ~ :. .. i 50 ~----~~----r+--------~----r·----~ ~ ;i :• ..... S i • :0- ; . i : i • ;I :• . i. . 25 ~---------4~i----'~r+-- ------~~-----+--•- -------------~ o 200 i ; ; ; i i I ; i 400 ••• I •• 600 Temperebn (F) Figure 1 - Typical Catalyst Light-off Curve 800 1000 This loss of activity could be the result of several phenomena acting alone or in combination. These situations include, halogen deactivation, poisoning of active catalyst sites with metals such as sulfur, silicone, phosphorous, or others, masking of active site by particulate, or thermal degradation. Each of these system degrading situations will be reviewed to see the cause and what methods are available to prevent them from occuring. 2 |