Analysis of the structural specificity of ZrO 2 nanoparticles in pillared clays by modeling the condensation process in
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0894-LL06-05.1
Analysis of the structural specificity of ZrO2 nanoparticles in pillared clays by modeling the condensation process in ZrOCl2*8H2O solutions N.V. Mezentseva, V.A. Sadykov, V.I. Avdeev, V.L. Kuznetsov. Boreskov Institute of Catalysis, pr. Lavrentieva, 5, Novosibirsk, 630090, Russia. ABSTRACT A combination of quantum-chemical approaches including DFT, semiempirical PM3 and molecular mechanics (force field ММ+) methods has been applied for analysis of the structure of polynuclear hydroxocomplexes of Zr in diluted solutions of its oxochloride as precursors of zirconia nanoparticles in zirconia-pillared clays. Relative stability of complexes differing by their size and shape has been estimated. INTRODUCTION Pillared clays containing in their interlayer space zirconia nanoparticles are promising as catalysts and supports for different petrochemical processes, selective reduction of nitrogen oxides by hydrocarbons in the excess of oxygen etc [1-4]. These materials possess a high thermal stability and a developed pore structure comprised of micropores (corresponding to galleries between aluminosilicate layers) and mesopores (generated due to faults in the clay sheets stacking). Pillared clays are obtained by the exchange of Na or K cations fixed in the interlayer space of clays with zirconium polynuclear hydroxospecies using diluted solutions of zirconium oxochloride. As dependent upon the synthesis conditions, the interlayer distance varies from 7 to 12-14 Å, which is caused by incorporation of two-dimensional or threedimensional Zr hydroxocomplexes [5]. Hence, properties of pillared clays are determined by the shape and structure of pillaring species. However, up to date, there is a lack of reliable information about characteristics of those cations in solutions. This works aims at predicting the most stable structures of those pillaring complexes by using a complex of quantumchemical computational methods. COMPUTATIONAL DETAILS The structure of crystalline Zr oxochloride (ZrOCl2*8H2O) is based upon the tetrameric unit [Zr4(OH)8(H2O)16]8+.. The first coordination sphere of Zr (CN=8) corresponds to the D2d symmetry [6]. For modeling the structure of pillaring species in solution, the Inorganic Crystal Structure Database (ICSD) [7] was used as a source of atomic coordinates in crystalline ZrOCl2*8H2O. In the first stage of modeling the condensation process occurring in the aqueous solution of ZrOCl2*8H2O, as a structural unit, charged [Zr4(OH)8(H2O)16]8+ tetramer was used. In this structure, Zr cations are bound by bridging hydroxyls (Zr-OH-Zr) situated below and under the plane of Zr cations. To satisfy the requirement of charge balance, tetramer was surrounded by solvated counter-ions Cl-. Preliminary estimation of charges on atoms of the tetramer and Cl- anions was carried out using a standard semiempirical PM3 method. In this approximation, only dimerization of tetrameric units was considered. In the second stage, for modeling condensation process leading to more complex structures, as a structural unit,
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