Polyfunctional Heterogeneous Catalysis

Differences between MFI- and MEL-Type Zeolites in Paraffin Hydrocracking

“…At 46% n-C 10 hydroconversion, this catalyst loses only 7% of the C 10 feed through hydrocracking (%C 10 hydrocracked, Table 1), whereas at that same conversion level the other catalysts lose more than 35% of the C 10 feed (5,(20)(21)(22). This low primary hydrocracking selectivity, the small amount of secondary hydrocracking (mol C 7 hydrocracked/100 mol C 10 hydrocracked) at a high % n-C 10 hydroconversion, and the high percentage of branched paraffins in the secondary hydrocracking product slate (1/5 7 x=4 % i-C x ) ( Table 1, also explains formula) all indicate that this particular MFI-type zeolite catalyst exhibits minimal mass transport and hydrogenation rate limitations (10,(41)(42)(43). The other tabulated MFI-type zeolite catalysts yield significantly less than 50% i-C 5 and have a high hydrocracking selectivity (Table 1).…”

“…It occurs when there are multiple transformations at acid sites inside pores that significantly limit sorbate mobility (14,28,38,40). This happens when the hydrogenation function is insufficiently active as compared to the acid function (38,(41)(42)(43) or when the mass transport between the hydrogenating sites and the acid sites is the rate-limiting step (18,38,41,43).…”

“…[4]), (iii) yield a primary C 5 fraction consisting of equal amounts of n-C 5 and i-C 5 (Eq. [4]), and (iv) have a low (primary and secondary) hydrocracking selectivity (10,(41)(42)(43). In practice, consecutive hydrocracking and hydroisomerization yield a secondary product slate interfering with a straightforward identification (19).…”

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

“…When this is the case, the product slate consists of a histogram with a single maximum indicative of preferential hydrocracking at the center of the chain, irrespective of the n-alkane feed length. 472,474,475,484,485 This is because the probability of formation of RRγ-trimethylalkene hydrocracking precursors is dependent on the proximity of the methyl groups to the center of the chain. [474][475][476]485 For reasons of symmetry, there are fewer permutations of their precursor transition state closer to the center.…”

“…472,474,475,484,485 This is because the probability of formation of RRγ-trimethylalkene hydrocracking precursors is dependent on the proximity of the methyl groups to the center of the chain. [474][475][476]485 For reasons of symmetry, there are fewer permutations of their precursor transition state closer to the center. For the system in Figure 51 we can therefore expect a product distribution dominated byproduct originating from 3,3,5-trimethylheptane and from 3,5-and 3,3-and 4,4-dimethyloctane (see Figure 53).…”