Aging of catalyst

Fig. 6. Catalyst inhibition mechanisms where ( ) are active catalyst sites the catalyst carrier and the catalytic support (a) masking of catalyst (b) poisoning of catalyst (c) thermal aging of catalyst and (d) attrition of ceramic oxide metal substrate monolith system, which causes the loss of active catalytic material resulting in less catalyst in the reactor unit and eventual loss in performance.

Figure 13. Correlation of bench activity data with engine dynamometer aging of catalyst B...

The ageing of catalysts is related to the above considerations, as far as the reactivity of the phases is concerned. Due to its crystal structure, the equilibrium shape of VPP is not platy but prismatic. As a consequence, platy VPP crystals age by thickening more and more with time and tend to become prismatic. It results in the decrease of the whole surface area but more particularly of the area of selective 100 faces, and consequently the selectivity to MA decreases. As in the case of -V0P04, the reduction of ai-V0P04 was shown to lead to prismatic-shaped crystals of VPP. On the contrary, crystals of 8 could be reduced to platy VPP crystals exhibiting... 

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