Nanocomposites Based Upon Alumina and Zirconia Pillared Clays Loaded with Transition Metal Cations and Clusters of Preci
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Mat. Res. Soc. Symp. Proc. Vol. 581 @2000 Materials Research Society
was added when required) and 0.1 M AlC13 starting solutions were used. The pillaring solutions obtained following earlier described procedures [5] as well as their suspensions with clay particles were aged at 60 'C for 16 h. By pillaring, up to 15 wt.% of alumina and ca 20 wt.% of zirconia (or CeO-ZrO 2 solid solution with - 1:1 ratio) were incorporated. Copper and cobalt cations were added using either cation exchange with corresponding nitrates solutions as in [1, 3] or impregnation. Silver was loaded either by wet impregnation or by the photoassisted deposition from nitrate solution using an ultraviolet radiation (a high pressure Hg lamp). Typically, up to 4 wt.% of Cu. 1% of Co and-1-2 wt.% of Ag were added to PILC. Bulk samples of highly dispersed (specific surface area - 180m2 /g) mesoporous tetragonal ZrO 2 partially stabilized by Ca, Sr and Ba (Me2" content - 3 at.%) were prepared by the ammonia coprecipitation from corresponding mixed nitrate solutions followed by the hydrothermal treatment at 100 TC in the presence of polyvinyl alcohol, drying and calcination at 600 'C. As bulk analog of alumina pillars, earlier studied [3] commercial 7-A120 2 (A-1 type) with the specific surface area - 180 m2/g was used. First copper (up to 1-4 wt.%) and cobalt (up to 1%) cations, then silver (up to 1-2%) were supported on the surface of these bulk systems from nitrate solutions by a standard wet impregnation procedure or photoassisted deposition from nitrate solution followed by drying and calcination at 600 'C. Samples were characterized using TEM (Jeol 200 C, 200 kv), EXAFS (spectra were acquired at the EXAFS Station of the Siberian Center of Synchrotron Radiation, Novosibirsk) combined with the X-ray diffraction (XRD, CuKa, an URD-63 diffractometer) and X-ray Small Angle Scattering (SAXS, a KMP-1 camera with CuKa radiation, nickel filter and an amplitude analyzer). Adsorption characteristics were measured on a Micromeritics ASAP2400 installation by N 2 adsorption at - 77 K. Surface properties were probed by the Infra-red spectroscopy of adsorbed CO test molecule (FTIRS, a Fourier-transform IFS 113V Bruker spectrometer). Temperature-programmed desorption of NO, (TPD) was carried out following procedures earlier described in details [2, 3]. Catalytic properties in the NO. SCR -HC and NO oxidation to NO 2 by 02 were tested in the flow microreactors using earlier described procedures [2-4] at GHSV 12000/h (0.1% C3H8+0.1% NO +1%02 in He), 18000/h (0.2%C 3 H6 + 0.2% NO + 2.5% 02 in N 2), 11200/h (0.05% C10H22 + 0.15% NO in air) and 30000/h (1% NO + 1% 02 in He). RESULTS Pore structure of pillared clays According to XRD, for all PILC the basal (001) spacing is in the range of 17-19 A, which corresponds to the gallery height - 8-9 A. The micropore volume estimated from the nitrogen adsorption isotherms (Fig. 1) was found to be - 0.1 cm 3/g, while the BET surface area was in the range of 200-320 m2/g, both values decreasing due to incorporation of transiti
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