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V(IV) Species, Location and Adsorbate Interactions in VH-SAPO-42 Studied by ESR and Electron Spin-Echo Modulation Spectroscopies

Back, Gern-Ho   (Department of Chemistry, Changwon National UniversityUU0001233  ); Yu, Jong-Sung   (Department of Chemistry, BK21 NanoBio Sensor Research Team, Hannam UniversityUU0001481  ); Lee, Hye-Young   (Department of Chemistry, Changwon National UniversityUU0001233  ); Kim, Min-Sik   (Department of Chemistry, BK21 NanoBio Sensor Research Team, Hannam UniversityUU0001481  ); Lee, Yong-Ill   (Department of Chemistry, Changwon National UniversityUU0001233  );
  • 초록

    Vanadium-incorporated aluminophosphate microporous molecular sieve VH-SAPO-42 has been studied by electron spin resonance(ESR) and electron spin-echo modulation (ESEM) spectroscopies to determine the vanadium location and interaction with various adsorbate molecules. The results are interpreted in terms of V(IV) ion location and coordination geometry. Assynthesized VH-SAPO-42 contains only vanadyl species with distorted octahedral or trigonal bipyramidal coordination. Vanadium incorporated into H-SAPO-42 occupied extra-framework site. After calcinations in $O_2$ and exposure to moisture, only species A is observed with reduced intensities. Species A is identified as a $VO(H_2O)_2^{2+}$ complex coordinated to three framework oxygen atoms bonded to aluminum. When hydrated VH-SAPO-42 is dehydrated at elevated temperature by calcination, species A loses its water ligand and transforms to $VO^{2+}$ ions coordinated to three framework oxygens (species B). Species B reduces its intensities significantly after treatment with $O_2$ at high temperature, thus suggesting oxidation of $V^{4+}$ to $V^{5+}$ . When dehydrated VH-SAPO-42 makes contact with $D_2O$ at room temperature, the ESR signal of species A is regained. The species is assumed as a $VO(O_f)_3(D_2O)_2$ by considering three framework oxygens. Adsorption of deuterated methanol on dehydrated VH-SAPO-42 results in another new vanadium species D, which is identified as a $VO(CD_3OH)_2$ complex. When deuterated ethylene is adsorbed on dehydrated VH-SAPO-42, another new vanadium species E identified as a $VO(C_2D_4)^{2+}$ , is observed. Possible coordination geometries of these various complexes are discussed.


  • 주제어

    SAPO .   Vanadium .   Molecular Sieve .   ESR .   ESEM.  

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