Synthesis, Characterization And Catalytic Property Of Zeolites With 12-membered Ring

Zeolite 13 and mordenite, which are possessed of I 2-membered ring channels, behave as outstanding catalysts in some chemical and petrochemical processes. It is an important target to improve these zeolites synthesis technology for extensively decreasing the cost. So far the study on their synthesis chemistry is far behind the commercial application. Few papers have been devoted to investigate for thermodynamics and kinetics of beta zeolite and high-silica mordenite, especially to systematidally examine in their crystallization mechanism. In this paper the synthesis of zeolite 13, mordenite with high Si02/A1203 molar ratio and rare earths containing mordenite in basic media with fluoride have been studied systematically. The product is further characterized by physicochemical methods.The crystallization process of zeolite f3 has been investigated by use of FT-IR, MAS NMR, XRD, DTG, SEM, and ICP-AES. The typical framework IR-absorptions patterns at 567 cm'and 518 cm~' have different nature. The former is detected at the initial induction period and its intensity changes a little in this period, but exhibits a direct correlation with crystallinity in growth period. The latter is not detected in induction period, but exhibits same trend in growth period. The n(Si02) / n(A1203) ratio of the solid phases obtained at 'different synthesis times changes significantly during the induction period, but changes a little in growth period. So the zeolite j13 crystal nucleus are formed via liquid-phase synthesis mechanism. A typical gel in synthesis of zeolite 13 is transformed initially into a solid, which contains richer aluminium, minor F and occluded TEA species. The aluminosilicate gel particles are dissolved by F during the induction period and the transition complex, which has aspecific weak X-ray diffraction peak at 2 0 22.80 and specific DTG pattern, is formed at turning point from induction period to growth period. During the growth period Si and Al transport from the liquid to the solid phase at almost same rates. F- anion has greater influence on the formation and turning of transition complex. The crystallization mechanism was presented as followed:The nanocrystalline zeolite 13 could be efficiently and economically synthesized in a wide range of Si02/Ab03 molar ratio (from 20 to 80 using commercial silica sol as silica source and from 20 to 400 using commercial water glass as silica source) according to crystallization mechanism in system of composite template. The new synthetic method of nanocrystalline zeolite in theory that the formation of crystal nucleus is controlled by structure directing agent was first presented.On basis of conclusion about the Si02/Al,03 molar ratio relationship between zeolite and gel, the aluminium-rich nanocrystalline zeolite 13 featuring a silica to alumina ratio near the theoretically lowest value (i.e, 14) was synthesized. A new- route synthesizing aluminium-rich nanocrystalline zeolite 13 was presented.The stability phase area for giving rise to a zeolite 13 phase and the regularity for nanocrystalline particles produced in the system wassystematically studied, in which tetraethylammonium hydroxide-fluoride was used as composite of template and silica sol and water glass as the silica source respectively. On basis of the described conclusion, the lowest level of TEAOHISiO2 ratio was extended to 0.04 by adjusting F! Si02 molar ratio and alkalinity.The stability phase area for giving rise to mordenite phase and some factors influencing the crystallization of siliceous mordenite in the absence amine but with fluoride was systematically studied. The results showed that the fluoride anion was the structure directing agent producing mordenite and mordenite formed via liquid-phase synthesis mechanism. The area of producing mordenite is broadened, the area of quartz obtained is reduced and mordenite appears together basically and the crystallization region towards ZSM-5 and ferrierite are no longer formed. The Si02/Al-,03 ratio of mordenite product can...