Shape-selective alkylation of biphenyl over H-[Al]-SSZ-24 zeolites with AFI topology

H-[Al]-SSZ-24 zeolites with AFI topology were synthesized through the alumination of [B]-SSZ-24 zeolites, and applied for the alkylation of biphenyl (BP). H-[Al]-SSZ-24 zeolites have high activity for the isopropylation. The shape-selective formation of 4,4'-diisopropylbiphenyl (4,4'-DIPB) occurred at moderate temperature; however, the selectivity for 4,4'-DIPB decreased with an increase in the reaction temperature. Isomerization of 4,4'-DIPB occurred at higher temperatures over internal and external acid sites when there are enough acid sites inside the channels. The channels can discriminate 4,4'-DIPB from the other DIPB isomers in their transition states; however, they can not prevent the isomerization of 4,4'-DIPB at higher temperatures. The selectivity for the least bulky 4,4'-dialkylbiphenyl increased with the bulkiness of alkylating agents in the order: isopropylation < s-butylation < t-butylation. These results strongly support the shape-selective formation of the least bulky products inside the channels of H-[Al]-SSZ-24 zeolites.