The Coke Deposits and Their Effects

It has been shown (Fig. 9) that for most of the molecular sieve catalysts the selectivity for isobutylene improves with TOS. Furthermore, it has been demonstrated with ferrierite that the change with TOS from the nonselective form (the noncoked state) to the selective form (the coked state) is accompanied by a change in the reaction mechanism from bimolecular to monomolecular. Here, the physicochemical properties of the molecular sieves and their variation with TOS are described and analyzed in terms of the correlations between the state of the molecular sieves and their activities and selectivities for n-butenc isomerization. 

When a ferrierite is used to catalyze the conversion of n-butenes, there is rapid coke deposition, as illustrated in Fig. 14. Several authors (51, 57) have shown that the coke deposition is rapid during the first hours of reaction in a flow system and much slower thereafter. The nature of the coke changes wfith TOS during the initial period, the coke is more aromatic 

The coke deposits affect the physical properties of the catalysts, as described in the following section. 

Xu et al. (57) compared the pore size distributions of fresh and aged HFER on alumina catalysts, showing that the mesoporosity does not change much with TOS. In contrast, the microporosity decreased substantially 

Change in the Coke Deposition and Coke Composition on a FER Catalyst as a 

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