Abstract
The isopropylation of biphenyl (BP) was examined over H-[Al]-SSZ-31 (SSZ-31) zeolites synthesized by hydrothermal synthesis (HTS) and dry-gel conversion (DGC). The synthetic method was found not to be the principal factor determining the shape-selective character of SSZ-31 zeolite, although the catalytic performance varied depending on the synthetic route employed. The least bulky isomers, 4-isopropylbiphenyl (4-IPBP) and 4,4′-diisopropylbiphenyl (4,4′-DIPB), were formed selectively over SSZ-31 synthesized by DGC and HTS. The selectivity for 4,4′-DIPB in the encapsulated products was higher than that in the bulk products over SSZ-31 by HTS; the isomerization of 4,4′-DIPB to the thermodynamically more stable 3,4′-DIPB occurred at external acid sites in the bulk products. This decrease in selectivity was not observed for SSZ-31 synthesized by DGC. The selectivity for 4,4′-DIPB in the bulk products decreased with increasing temperature above 275 °C, whereas, that for the encapsulated product increased. The reaction is considered primarily to occur inside the pores at all temperatures, in particular near the pore mouth, and at high temperatures, to increase the participation of deep acid sites away from the pore mouth due to increased diffusion of products. SSZ-31 was also found to be more selective in s- and t-butylations with 2-methylpropene and 1-butene than in isopropylation due to steric factors.
Published Version
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