Synthetic investigation on MCM-68 zeolite with MSE topology and its application for shape-selective alkylation of biphenyl

The synthesis of MCM-68 zeolite with MSE topology, which is a three-dimensional zeolite with 12 × 10 × 10 membered ring (MR) channel systems was tuned under the hydrothermal conditions using N,N,N′,N′-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium diiodide as SDA, and applied for the isopropylation of biphenyl (BP). The H+ form zeolite (SiO2/Al2O3=26) was obtained by the ion-exchange of as-synthesized sample (SiO2/Al2O3 = 20) after the calcination, and the zeolites with SiO2/Al2O3 = 70–263 were prepared by the dealumination of calcined sample (SiO2/Al2O3 = 20) by 1 N hydrochloric acid.Catalytic activities in the isopropylation of BP were enhanced by the dealumination of MCM-68 zeolite, and maximized at SiO2/Al2O3 = 70. However, further dealumination accompanies the decrease in the catalytic activity. The selectivity for 4,4′-diisopropylbiphenyl was ca 75–80% for all MCM-68 zeolites at moderate temperatures up to 300 °C. These high selectivities are due to restricted transition state mechanism inside the 12-MR straight channels: BP cannot easily enter into the 10-MR channels and cages of the zeolites.The selectivity for 4,4′-di-sec-butylbiphenyl and 4,4′-di-tert-butylbiphenyl improved in sec-butylation and tert-butylation of BP compared to the isopropylation. The exclusion of bulky isomers was enhanced by increasing the bulkiness of the alkylating agents.