Sepiolites as supports for Pd catalysts used in organic reduction processes

Multinuclear Magnetic Resonance Spectroscopy Studies of the Structuration of the Tunnels of Sepiolite in the Presence of Intracrystalline Pyridine Molecules

Sepiolite, a naturally occurring magnesiosilicate nanoporous clay mineral with a tunnel structure, contains two types of water molecules in the structure: zeolitic water trapped inside the tunnels and structural water molecules which interact strongly with magnesium cations. The zeolitic water was removed by heating the sepiolite to 120 degrees C. The partially dehydrated sepiolite absorbed pyridine vapor to produce an intercalated material where the pyridine takes the place of the zeolitic water. 1H solid-state MAS NMR spectroscopy showed that there is isotopic H/D exchange between pyridine-d5 and the remaining structural water molecules of the sepiolite framework. The exchange takes place at room temperature over several days. Wide line solid state 2H NMR of the sequestered pyridine-d5 showed that two populations of pyridine molecules coexist in the material: one very mobile physisorbed population, which can be removed by heating at 90 degrees C, and a population due to pyridine trapped in the tunnels. Except for small in-plane librations, the trapped pyridine was shown to be held rigidly by the sepiolite. When the pyridine intercalated material is heated at 400 degrees C the structural water and some of the pyridine is lost. The remaining pyridine takes the place of the structural water to produce a new inorganic-organic nanohybrid material with the pyridine bound to the terminal Mg(II) in the structure. The pyridine in this material as well as the intercalated material was characterized by slow-spinning 15N and 13C CP/MAS NMR spectroscopy. The 15N NMR was shown to be a very sensitive probe to characterize the various types of pyridine. The data indicate that pyridine molecules in the inorganic-organic nanohybrid material are directly bound to magnesium cations exposed in the tunnels of sepiolite.

Characterization of the Structure and Catalytic Activity of Pt/Sepiolite Catalysts

Four catalysts containing 1% w/w Pt deposited on various sepiolite supports were prepared. Two natural sepiolites and another two obtained by acid treatment of one of them were used. Both the sepiolites used as metal supports and the catalysts were characterized for structure and surface properties, using (1)H and (29)Si MAS NMR spectroscopy, and (29)Si CP/MAS NMR spectroscopy, in addition to hydrogen, pyridine, and CO(2) chemisorption measurements. The activity of the catalysts in the hydrogenation of benzene to cyclohexane and the dehydrogenation of cyclohexane to benzene was examined and the catalyst supported on the natural sepiolite called Pangel was found to be the most active of all. Copyright 2000 Academic Press.

Characterization of Spanish sepiolites by high-resolution solid-state NMR

29Si NMR (MAS and CP/MAS) and 1H MAS NMR techniques were used to characterize four sepiolites, two of natural origin (commercialized under the names Pangel and Pansil) and the other two obtained from them by treatment with 2 M or 4 M H2SO4, respectively. These techniques were used to identify the structural and surface changes undergone by sepiolites by the effects of acid treatment and calcination. Various types of Si were detected; also, treatment with 4 M H2SO4 destroyed the sepiolite and produced fibrous silica.