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RISS 인기검색어
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- 저자 : Tzitzios, Vasilios (검색결과 1 건)
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Katsiotis, Marios S.,Fardis, Michael,Al Wahedi, Yasser,Stephen, Samuel,Tzitzios, Vasilios,Boukos, Nikolaos,Kim, Hae Jin,Alhassan, Saeed M.,Papavassiliou, Georgios American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.6
<P>A nanosized HY zeolite was synthesized and studied by means of <SUP>1</SUP>H and <SUP>27</SUP>Al NMR during thermal dehydration in the temperature range 20–600 °C. The nanozeolite is comprised of a mixture of well-crystallized ultrathin platelets and octahedral nanocrystals, dressed with pentacoordinated extraframework Al<SUP>(V)</SUP>. <SUP>1</SUP>H NMR spin–lattice (<I>T</I><SUB>1</SUB>) and spin–spin (<I>T</I><SUB>2</SUB>) relaxation measurements in combination with <SUP>27</SUP>Al 3Q-MAS NMR reveal two different interaction paths between water molecules and the nanozeolite solid matrix: (i) water molecules strongly interacting with Al<SUP>(V)</SUP> cations, indicated by the high <I>T</I><SUB>1</SUB>/<I>T</I><SUB>2</SUB> ratio, and (ii) water molecules with amply smaller <I>T</I><SUB>1</SUB>/<I>T</I><SUB>2</SUB> ratio, interacting moderately with Al<SUP>(IV)</SUP> and Al<SUP>(VI)</SUP> cations. Relevant measurements on bulk HY rich in extraframework Al<SUP>(VI)</SUP> show the presence of the second relaxation channel only, indicating that the enhanced water adsorption observed for the nanozeolite originates partly from its extended surface and partly from the Al<SUP>(V)</SUP> decoration. Al<SUP>(IV)</SUP> sites in the nanozeolite appear to be highly resilient during heating, even while the framework starts to collapse and Al<SUP>(VI)</SUP> transforms to Al<SUP>(V)</SUP>. Finally, <SUP>1</SUP>H NMR shows that water protons interact particularly strongly with the Al sites in the nanozeolite at temperatures as high as 500 °C, unveiling the important role of the Al<SUP>(V)</SUP> decoration on this nanocatalyst.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-6/jp513030w/production/images/medium/jp-2014-13030w_0013.gif'></P>
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