Title : Zirconium containing ionic materials as catalysts for C3, C4 alcohols conversions
Abstract:
Zirconium containing ternary phosphates Na(Cs)1-2xMxZr2(PO4)3 (NASICON-family) and ternary oxides (vismuth vanadates Bi4V2–2xZr2xO11–δ of perovskites family) in investigated series of compositions are studied for the vapor-phase selective dehydration and dehydrogenation of isobutanol and isopropanol in the temperature range 200-400 0C. These groups of catalysts represent the solid electrolytes (SE) with cationic and anionic conductivity respectively. The cations M(+2) = Co, Ni, Cu partially substitute the conducting ions Na+ or Cs+. For SE-catalysts characterization the methods XRD, XPS, IR, UVS, SEM, TEM, acidity/basicity surface titration were used. The results demonstrate the correspondence of NASICON frame structures for all of complex phosphates obtained, changes in surface composition vs bulk, different acid/basic sites in M presence and coordination of adsorbed alcohol molecule with hetero-linkages active site V-O-Zr in BIZRVOX. It is found the highest activity for a highly conductive γ-phase of BIZRVOX with selectivity 85–100% for isobutanal formation. The observed step-wise Arrhenius dependences for dehydrogenation reaction are related to changes in the conducting properties of the catalyst. The apparent activation energy decreases linear with phase transformation when Zr content increases. It is found that Cs-Zr-phosphates catalysts prepared by sol-gel procedure showed high selectivity in isobutene formation. But the nature of ion-dopant M as active site is very important too. We found the linear correlation between activation energy (Ea) for isopropanol dehydrogenation reaction (model reaction) and ionic radius of substituting ions M=Ni,Co,Cu in Na-Zr-phosphates prepared by solid phase synthesis. When temperature rises, the change in position M in conductive channel occurs and Ea value of alcohol dehydrogenation reaction diminishes. So, there are many examples confirming the relationship between conductive and catalytic properties of ionic’s materials.
