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Jo, Changbum,Cho, Kanghee,Kim, Jaeheon,Ryoo, Ryong The Royal Society of Chemistry 2014 Chemical communications Vol.50 No.32
<P>The synthesis of a mesoporous material with uniform mesopore diameters and crystalline MFI zeolite walls has been achieved, simply by seeding the multiammonium surfactant-directed synthesis with bulk zeolite crystals. The bulk seeds disappeared in the final product. As a result of seeding, the mesoporous zeolites could be generated rapidly even at high Al content.</P> <P>Graphic Abstract</P><P>The synthesis of a mesoporous material with uniform mesopore diameters and crystalline MFI zeolite walls has been achieved, simply by seeding the multiammonium surfactant-directed synthesis with bulk zeolite crystals. The bulk seeds disappeared in the final product. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cc01070a'> </P>
Jung, Jinhwan,Jo, Changbum,Mota, Filipe Marques,Cho, Jangkeun,Ryoo, Ryong Elsevier 2015 Applied Catalysis A Vol.492 No.-
<P><B>Abstract</B></P> <P>Mesopores with zeolite walls were generated through desilication of bulk crystals of MFI zeolite in a NaOH solution in the presence or absence of cetyltrimethylammonium surfactant, as reported in the literature. Catalytic functions of the Brønsted acid sites existing on the mesopore walls were evaluated in comparison with external surfaces of 2.5-nm thick MFI zeolite nanosheets, which were hydrothermally synthesized using a meso-micro dual structure-directing surfactant. Acid sites were characterized with respect to the strength and concentration by <SUP>31</SUP>P NMR signals of adsorbed tributylphosphine oxide. Catalytic functions were evaluated for decalin cracking, and acetal formation of benzaldehyde with pentaerythritol. The result from desilication was quite sensitive to the particle diameters of the initial zeolite samples. In our best case of desilication, the mesopore walls exhibited similar catalytic activity for the acetal formation to the external surfaces of MFI nanosheets. In contrast to the condensation reaction occurring at mild or moderate acid sites, the result for decalin cracking requiring strong acid sites indicated that the desilicated zeolite corresponded to about 60% of the MFI nanosheets.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hierarchical zeolites with similar mesoporosity are synthesized by different methods. </LI> <LI> According to method, concentration and strength of external acid sites are different. </LI> <LI> Zeolite synthesized by structure-directed synthesis excelled in decalin cracking. </LI> </UL> </P>
Zeolite nanosheet of a single-pore thickness generated by a zeolite-structure-directing surfactant
Jung, Jinhwan,Jo, Changbum,Cho, Kanghee,Ryoo, Ryong The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.11
<P>Zeolite MFI nanosheets have been hydrothermally synthesized using a surfactant with the formula [C<SUB>18</SUB>H<SUB>37</SUB>–N<SUP>+</SUP>(CH<SUB>3</SUB>)<SUB>2</SUB>–C<SUB>6</SUB>H<SUB>12</SUB>–N<SUP>+</SUP>(CH<SUB>3</SUB>)<SUB>2</SUB>–C<SUB>6</SUB>H<SUB>12</SUB>–N<SUP>+</SUP>(CH<SUB>3</SUB>)<SUB>2</SUB>–C<SUB>18</SUB>H<SUB>37</SUB>][Br<SUP>−</SUP>]<SUB>3</SUB> as the zeolite structure-directing agent. These nanosheets correspond to a slice of MFI zeolite crystal of 1.5 nm thickness in the <I>b</I>-direction. Each nanosheet is composed of a monolayer of micropores, which is thinner than a single crystal unit-cell dimension (2.0 nm). Such a single-pore zeolite nanosheet still exhibits high thermal stability, steam stability, acid strength and shape-selective catalytic activity, comparable to the bulk crystal.</P> <P>Graphic Abstract</P><P>Zeolite nanosheet of a single-pore thickness (1.5 nm) was synthesized by using a Gemini-type surfactant as the zeolite structure-directing agent. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm16539b'> </P>
Tomographic imaging of pore networks and connectivity of surfactant-directed mesoporous zeolites
Lee, Seungyeop,Jo, Changbum,Ryoo, Ryong The Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.22
<P>Zeolites of MFI, MTW, *MRE and beta frameworks were synthesized by a method using micropore-mesopore dual generating surfactants. The porous texture of the zeolites was characterized by electron tomography and argon adsorption after the removal of the surfactant by calcination. For high-contrast tomography, the zeolites were supported with platinum. The resultant tomograms showed disordered and interconnected networks of Pt nanowires and nanosheets, which corresponded to the shape of the surfactant-directed mesopores. In the calcined zeolites, both the mesopores and zeolitic micropores were fully accessible for argon adsorption. Before calcination, however, no pores were accessible even after being thoroughly washed with solvent. The result indicated that the surfactant head could be tightly encased within the micropores after guiding the formation of the zeolite framework as a part of the mesopore wall, so that the surfactant was difficult to remove by solvent washing. After calcination, the micropores and mesopores could be connected through an aperture in which the neck of the surfactant molecule had been located. Neohexane was adsorbed very rapidly due to the micropore-mesopore connectivity. The hierarchical pore connectivity is an important and characteristic feature of the surfactant-directed zeolites for application in high performance adsorption and catalysis.</P>
Sulfonium-based organic structure-directing agents for microporous aluminophosphate synthesis
Lee, Sungjune,Jo, Changbum,Park, Hongjun,Kim, Jaeheon,Ryoo, Ryong Elsevier 2019 Microporous and mesoporous materials Vol.280 No.-
<P><B>Abstract</B></P> <P>Sulfur-centered phenyl, <I>n</I>-butyl, <I>p</I>-tolyl, and benzyl sulfoniums and sulfides were tested as organic structure-directing agents (SDAs) for the synthesis of crystalline microporous aluminophosphates (AlPOs) over various ranges of gel compositions, hydrothermal treatment temperatures, and crystallization times. Among the investigated compounds, triphenylsulfonium gave single-phase products of ATS-type AlPO and silicoaluminophosphate. Other sulfoniums yielded only non-porous, dense crystalline AlPOs. On the other hand, diaryl sulfides gave a tiny amount of AFI-type AlPO amid tridymite and amorphous phases. Based on the results, it was found to be reasonable that weakly basic sulfide could hardly act as a zeotype SDA due to the low protonation to sulfonium at the present synthesis pH.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Various sulfoniums and sulfides were tested as SDAs for synthesis of zeotype AlPOs. </LI> <LI> Triphenylsulfonium hydroxide SDA gave single-phase ATS-type AlPO and SAPO. </LI> <LI> Sulfides were unsuitable to serve as an AlPO SDA due to insufficient basicity for protonation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>