Synthesis, Characterization And Catalytic Performance Of Hierarchical Micro- Mesoporous Composited Zeolites

The hierarchical micro-mesoporous composite materials combined the free diffusion ability of the mesoporous material and the high thermal/hydrothermal stability,acid activity of the microporous zeolite.Therefore,this kind of material not only possessed the activity and the stability of conventional molecular sieve,but also overcame the diffusional limitation and prevented the deactivation caused by the carbon deposition of catalyst.As a result,the hierarchical micro-mesoporous composite materials were the research hotspots in recent years.This study used two types of long chain quaternary ammonium salt which were hexadecyl trimethyl ammonium bromide?CTAB?and[C₁8H₃7-N+?CH₃?₂-C₆H₁2-N?CH₃?₂]Br^-(C₁₈N)as organic structure directing agent?OSDA?,aluminum sulfate octadecahydrate?Al₂?SO₄?₃·18 H₂O?as aluminum source,tetraethyl orthosilicate?TEOS?as silicon source.The final molar composition of the synthesis mixture was6 CTAB:50 SiO₂:20 NaOH:6350 H₂O:x Al₂?SO₄?₃.As a result,we synthesized the hierarchical micro-mesoporous MFI-type composite materials using one-pot method successfully.The samples were characterized by methods such as power X-ray diffraction?PXRD?,FT-IR Spectrometer?FT-IR?,Solid-state NMR?Solid NMR?,Nitrogen physical adsorption,Transmission electron microscopy?TEM?and Scanning Electron Microscope?SEM?.The results of characterizations confirmed the zeolitic framework possessed both mesopore and micropore,and the mesoporous size was adjustable along with the reaction condition.The results indicated that the hierarchical aluminosilicate zeolites with different ratios of Si/Al were simply synthesized by a temperature-gradient strategy using conventional CTAB as single structure directing agent.The ordered two-dimensional mesoporous MCM-41 material was synthesized at 100? for 3 days.The zeolites contained both the ordered two-dimensional mesoporous MCM-41 and the crystallized microporous MFI were synthesized at 100?for 3 days and the 160?for 6-8 days.In addition,the catalytic conversion involving large orgnic molecules using the prepared MFI-type micro-mesoporous materials in the aldol condensation between benzaldehyde and 2-hydroxyacetophenone was tested.The reaction results showed that the hierarchical zeolites exhibit outstanding catalytic performance with a conversion as high as 73%.Hierarchical aluminosilicate zeolites were synthesized using[C₁8H₃7-N⁺?CH₃?₂-C₆H₁2-N?CH₃?₂]Br^-(C₁₈N)as single structure directing agent.The three-dimensional?3D?wormhole frameworks were obtained at 160? for 4 days.The micro-mesoporous composited zeolites contained the 3D wormhole structure and crystallized microporous MFI,which were prepared at 160?for 12 days,the catalytic performance could reach to 89.8%,which was a new record for the reaction.