Study On Endo-to Exo-Isomerization Of Tetrahydrodicyclopentadiene Catalyzed By Y Zeolites

This paper is dedicated to the isomerization from Endo-tetrahydrodicyclopentadieneto Exo-tetrahydrodicyclopentadiene catalyzed by zeolitic catalysts, which is focusedon the influences of zeolites characteristics, zeolites modification and reactionconditions. Finally the research is specialized on the regeneration of catalysts.The catalytic activities of zeolites are mostly determined by the size of pores channelsand acidity distribution. With calcinations temperature considered, different zeolitesand Y zeolites with different Si/Al and cations were tested. The results show thatH-USY zeolites calcined at 450°C are most favorable because of its large porechannel (0.74nm) and large amount of middle acidic sites.The modification of H-USY and H-SSY by moderate F or NiO loading improvecatalytic activities of parent zeolites. The NH3-TPD curves of F modified Y zeolitesshowed that F loading and calcinations temperature influence the acidity distribution.The involvement of F decreases strong acidic sites while increase middle strongacidic sites, which leads to the improvement of Yexo and Sexo, the decrease of ADMbyproduct. In all modified catalyst, F loading H-SSY (NH4F/SSY=6.62%) calcined at500°C show best catalytic activity.The optical reaction conditions are as followed: Endo-THDCPD/Cat=40.5g/9.00g,temperature 195°C, air atmosphere. The Endo-conversion , Exo-yield andExo-selectivity are 96.46%,93.12% and 96.54% respectively. After reaction, thecatalysts need to be regenerated to recover its activity. The regeneration results showthat both unmodified and F modified zeolites can recover its activity after severalreuse and regeneration. Trace amount of oxides can poison the acidic sites whiledeposit can block the channel of zeolites, which leads to the deactivation of catalyst.Finally, the mechanism of isomerization is discussed. The concentration of THDCPD+is most influential factor. Low concentration of THDCPD+ tends to formExo-THDCPD+, which is more favorable in reaction kinetics, while highconcentration of THDCPD+ favors the formation of ADM+, which is more stable inthermodynamics. That's reason why acidic sites with middle acidity favor theformation of Exo-THDCPD.