Catalytic Cracking of Endothermic Hydrocarbon Fuels over Ordered Meso-HZSM-5 Zeolites with Al-MCM-41 Shells

摘要

Ordered meso-HZSM-5 zeolites with Al-MCM-41 shells were synthesized by a surfacant-directed encapsulating process. It was found that ordered meso-HZSM-5, which was used as a core, could be synthesized using a designed amphiphilic organosilane as a surfactant and that the mesopore size of the MCM-41 shell can be adjusted from 2.5-3 to 4.5-10 nm by changing the structures of alkyltrimethylammonium bromide and the trimethylbenzene amount. Catalytic cracking performances of supercritical n-dodecane (500 degrees C and 4 MPa) show that ordered meso-HZSM-5 zeolites with Al-MCM-41 shells of 4.5-10 nm exhibit a 28% higher catalytic activity and a 25% lower deactivation rate compared to the conventional HZSM-5 zeolites. With an increasing mesopore size of the MCM-41 shell, the acid sites accessibility increased gradually and, thus, led to enhanced catalytic activity and decreased secondary reaction ability. In addition, ordered hierarchical zeolites show a well connection of ordered mesopores between the core and shell, which could also lead to the enhanced acid site accessibility.