Synthesis of cyclopentadiene trimer (tricyclopentadiene) over zeolites and Al-MCM-41: The effects of pore size and acidity

Cyclopentadiene trimer (tricyclopentadiene) is an important raw material during the synthesis of high-energy-density fuel. In this study, tricyclopentadiene was synthesized through a [4+2] cycloaddition between endo-dicyclopentadiene and cyclopentadiene over microporous zeolites (ZSM-5, HY) and mesoporous Al-MCM-41 catalysts. The catalytic activity was strongly influenced by the average pore size and the Brönsted acidity of the catalyst. Of the tested catalysts, the NH₄F-treated Al-MCM-41 catalyst, which had meso-sized pores (3.4 nm in average) and enhanced Brönsted acidity, exhibited the best dicyclopentadiene conversion, tricyclopentadiene selectivity and yield. The average pore size of the catalyst also influenced the isomer distribution of the tricyclopentadiene products: the mesoporous catalysts produced mixtures of exo- and endo-tricyclopentadiene, which favored the exo-fraction (approximately 40 mol%) compared to the microporous catalysts (approximately 20 mol%). The differences in the reaction pathways followed by the zeolites and Al-MCM-41 catalysts were discussed. To investigate the structural and acidic properties of the catalysts, various characterization techniques were applied, such as low-angle X-ray diffraction, N₂ adsorption-desorption, ammonia temperature-programmed desorption, and Fourier transform-infrared spectroscopy of adsorbed pyridine.