Dimerization of Bicyclo[2.2.1.]hepta-2,5-diene Over Various Zeolite Catalysts

The activities of HY, Hbeta, HZSM-5 and mesoporous Al-MCM-41 catalysts were evaluated during the dimerization of bicyclo[2.2.1]hepta-2,5-diene (norbornadiene, NBD). This study focuses on the effects of the pore structure and acidity of the catalysts on the NBD dimerization reaction. When conducting the NBD dimerization reaction over the HY, Hbeta, HZSM-5 and Al-MCM-41 catalysts, it was confirmed that NBD dimer (NBDD) synthesis could be facilitated at a temperature of 250 °C, whereas NBD scarcely reacts through a thermal reaction without a catalyst. Although the NBD conversion rates of the four catalysts are nearly identical after a 12-h reaction, the HY zeolites showed much higher selectivity to NBDD than those with the Hbeta, HZSM-5 and Al-MCM-41 catalysts. The HY catalyst showed the highest yield, reaching 41.5 wt% after a 12-h reaction. The higher selectivity of the HY catalyst during the dimerization of NBD could be explained in terms of its appropriate pore structure and by the higher concentration of Brønsted acid sites. The present study reveals that the HY zeolite is a potential heterogeneous catalyst for NBDD synthesis through the dimerization of NBD at a high yield.