Synthesis, crystal structure, characterization, and catalytic properties of TNU-9.
The synthesis, crystal structure, characterization, and catalytic properties of the novel medium-pore zeolite TNU-9 (framework type TUN), one of the most crystallographically complex zeolites known to date, are described. TNU-9 was found to crystallize under hydrothermal conditions at the expense of a lamellar precursor over a very narrow range of SiO(2)/Al(2)O(3) and NaOH/SiO(2) ratios and in the presence of 1,4-bis(N-methylpyrrolidinium)butane and Na+ ions as structure-directing agents. A combination of molecular modeling and Rietveld refinement using synchrotron powder diffraction data confirms the proposed topology of as-made TNU-9 and suggests three or possibly four different sites for the organic within the complex pore structure. The proton form (H-TNU-9) of this new medium-pore zeolite exhibits exceptionally high hydrothermal stability, as well as very strong acidity. When compared to H-ZSM-5, H-MCM-22, H-mordenite, and H-Beta, H-TNU-9 displays unique shape selectivities for the acid-catalyzed reactions of monoaromatic hydrocarbons such as the disproportionation of toluene and the isomerization and disproportionation of m-xylene. In particular, for the isomerization of m-xylene, the ratio of isomerization to disproportionation increases steadily to values in excess of 50 with prolonged time on stream and a high p/o xylene ratio is observed in the products, achieving a value of ca. 6 after only a short time on stream. These results are rationalized on the basis of the unique pore topology of TNU-9.
Hong
Suk Bong
SB
School of Environmental Science and Engineering, POSTECH, Pohang 790-784, Korea. sbhong@postech.ac.kr
Min
Hyung-Ki
HK
Shin
Chae-Ho
CH
Cox
Paul A
PA
Warrender
Stewart J
SJ
Wright
Paul A
PA
D002384:Catalysis; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D012822:Silicon Dioxide / Q000737:chemistry*; D017641:Zeolites / Q000737:chemistry*
D017641:Zeolites; D012822:Silicon Dioxide