Synthetic And Characterization Of Hierarchical Porous Composite Zeolites With Microporous And Mesoporous

Hierarchical porous composite zeolites improve morphology and acidity distribution of single zeolite and taking each advantage of microporous and mesoporous, which show different catalytic properties in catalysis with the synergy of the two porous structures. The paper focuses on ZSM-5/EU-1composite zeolite with embedding structure and it was synthesized by using acid pre-treating EU-1 seeds by two steps hydrothemal crystallization. The result revealed that surface acidity and skeleton structure of seeds was influenced by acid pre-treating, which contributed to ZSM-5 nucleation and growing within EU-1 agglomeration. Composite ZSM-5/EU-1 contain both microporous(with diameter 0.82nm) and mesoporous(with diameter distribution between 1.42 nm and 2.20nm) hierarchical-porous, strong acid amount relatively increasing after being compounded. In the process of methanol conversion catalysis,ZSM-5/EU-1 composite zeolite with embedding structure shows good catalyticperformance, the ratio of methanol conversion is 98.16%, the ratio of xylene in the distribution of aromatics products is 64.65% and p-xylene distribution among xylene is further enhanced while comparing to mechanical mixture zeoliteCore-shell composite zeolite shows good catalytic properties because of its special core and shell structure and appropriate acidity distribution and porous structure. High crystallinity and purity ZSM-5/EU-1 core-shell intergrowth zeolite was synthesized by dual-template with appropriate citriate adding, the results indicated that EU-1 zeolie grew around ZSM-5 surface defects, the amount of strong acidity in core-shell zeolite is relatively increased comparing with single zeolite and the composite zeolite was composed of well-fused, the microporous with 0.94 nm in diameter and mesoporous structure appeared between 1.24 nm and 1.84 nm in diameter, which apparently is lager than ZSM-5/EU-1 composite zeolite with embedding structure. Optimum synthesis condition was gained by analyzing the synthetic process:n(citrate)/n(Al2O3)=0.8~1.2,appropriate pH and crystallization time respectively are 10.5~11.5 and 72~96h. The possible growth process of core-shell composite zeolite is: Firstly ZSM-5 crystal was formed, Then, with time prolonging and the guiding effect of HMBr2, basic structure units of EU-1 was formed and grew around ZSM-5 surface defects. Thus, core-shell ZSM-5/EU-1zeolite was formed.In the process of methanol conversion to p-xylene catalysis, the catalytic products selectivity of core-shell zeolite is obviously higher than mechanicalmixture and the p-xylene selectivity of core-shell zeolite is continually improving with the increasing of addition of citrate.Beta zeolite has high methnaol conversion with its 12-membered ring special porous and strong activity. EU-1/β hierarchical porous composite was synthesized according to the structural similarity and porous characteristics of both EU-1 and β zeolite, which increased the ratio of methnaol conversion and was applied to maromolecule catalysis. EU-1/β composite zeolite was synthesized by preset crystal seed method by using EU-1 seed and tetra-ethylammonium hydroxide as template among alkalic system, finding that Beta zeolite adhered to EU-1 zeolite surface and it contains both microporous(about 0.82 nm in diameter) and mesoprous(about 2.20 nm in diameter) simultaneously, its acidity and acid amount is higer than mechnical mixture, its appropriate synthesis condition is 10%~20% seeds addition, alkali and template content in a range of n(OH-)/n(SiO2)=0.24~0.48, and n(TEAOH)/n(SiO2)=0.55~0.68 and appropriate crystallization time is 72h~96h.