Deactivation modes zeolite effect

Deactivation of zeolites, like that of the other porous catalysts occurs in two ways, the first one in which at the maximum one active site per coke molecule is deactivated, the second in which several active sites are deactivated. The two modes of zeolite deactivation are shown in Figure 7. The effect of coke on the activity and on the pore volume accessible to the reactant is also indicated. 

In addition, oxidized V also catalyzes coke and H2 formation through dehydrogenation as described in the case of Ni. V is therefore a significant contributor to catalyst deactivation, Figure 5.6. In addition, the more oxidized the V, the more destructive the effect if, therefore, the regenerator is operated in the more efficient full burn mode (lower levels of CO emissions), the destruction of the zeolite is increased, Figure 5.7. 

The effects of the pore structure on the toxicity of coke molecules can be explained by differences in the significance of the modes of deactivation from one zeolite to another ... 

We have used the CPAP technique in two unrelated deactivation investigations. The experimental procedures and analyses are tailored to the individual processes. We show the effect of temperature and coke level in the relative magnitudes of site suppression and pore choking in deactivation by coking during cumene cracking over a zeolite catalyst, and relate results to a simple physical model. For HT of CDL over a supported multimetal catalyst, we show that site suppression is the predominant mode of deactivation by deposition of carbonaceous and metallic materials, at least at large times on stream. 

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