The Synthesis Of Hierarchical Zsm-5Zeolite And The Performance In Methane Dehydroaromatization

In the research of the directly catalytic transformation of methane, methane dehydro-aromatization(MDA) is a very important way. Although the reaction mechanism of research and improvement of the catalyst has achieved great development, but the carbon deposition which causes catalyst deactivation in the MDA transformations is still one of the challenges. Hierarchical zeolite has a excellent mass transfer ability, its applications in MDA is one of the active fields.In this article, we adopted static hydrothermal method, dynamic hydrothermal method, two stage varying temperature hydrothermal method and vapor-phase method to synthetize hierarchical ZSM-5zeolites. In the process of synthesis, low-priced sodium silicate for the silicon source and aluminum sulfate for the aluminum source were used without the second template agent to synthetize hierarchical ZSM-5zeolites. The main content and conclusions were as follows:(1) In the static hydrothermal condition, we adjusted the crystallization time and crystallization temperature to synthetize hierarchical ZSM-5zeolites, the size was0.5-1.4μm, the zeolites were assembly formed by small particle size crystals and generated intercrystalline pore, mesoporous mainly came from intercrystalline pore. When used in MDA, the CH4conversion was14%, higher than conventional catalyst.(2) In the constant temperature dynamic hydrothermal condition, we fastly synthetized hierarchical ZSM-5zeolites, the size was1-1.5μm. When used in MDA, the CH4conversion was15.9%, it was3percentage point higher than conventional catalyst.(3) In the two stage varying temperature dynamic hydrothermal condition, we simpled synthetized hierarchical ZSM-5zeolites, the size was0.8-1μm. When used in MDA, the initial CH4conversion was18.5%, it was5.5percentage point higher than conventional catalyst, after24h, the CH4conversion still was higher than8%.(4) In H2O vapour phase condition, we synthetized ZSM-5zeolites with unform size, the size dimension was150-250nm, and the specific surface area was very large. When used in MDA, the initial CH4conversion was17.5%, it was4.5percentage point higher than conventional catalyst.