Titania-supported catalysts preparation

Santos J, Phillips J, Dumesic J (1983) Metal support interactions between iron and titania for catalysts prepared by thermal-decomposition of iron pentacarbonyl and by impregnation. J Catal 84 147... 

Fig. 3. Niteogen adsorption isotherms (A) and the corresponding BJH pore size distribution curves (B) of the mesoporous titania as-prepared (MTi02 80), modified by ceria mesoporous titania support as-prepared (CeMTi 80) and calcined at 400 °C (CeMTi 400), and gold-based catalysts calcined at 400 °C with different gold content (2 Au/CeMTi 400 and 5 Au/CeMTi 400).

In titania-supported catalysts, both unpromoted and promoted with potassium, the support-applied phase interaction is too strong, causing the formation of various mixed oxides. T ese solid phase reactions are observed both during preparation and during the test reaction. This is reflected in the catalytic performance, which displays a fatal deactivation within a short period of time. 

The preparation method of titania support was described in the previous paper [6]. Titanium tetraisopropoxide (TTIP 97%, Aldrich) was used as a precursor of titania. Supported V0x/Ti02 catalysts were prepared by two different methods. The precipitation-deposition catalysts (P-V0x/Ti02) were prepared following the method described by Van Dillen et al. [7], in which the thermal decomposition of urea was used to raise homogeneously the pH of a... 

Figure 1. TEM image of a titania supported gold catalyst (1.7wt.% Au) prepared by deposition-precipitation (gold particle size = 5.3+ 0.3 nm, dispersion = 36%). (Reprinted from Reference [84], 2000, with permission from American Chemical Society).

The reduction of the catalyst precursor with sodium formate resulted in a lower Pd dispersion than the catalyst prepared by hydrogen reduction, the particle size is much larger in the former catalyst. The mesoporous carbon supported Pd catalysts are near to those of Pd on titania with respect to their enantiodifferentiating ability. Besides the metal dispersion, the availability of the Pd surface in the pores for the large modifier molecules seems to be the determining factor of the enantioselectivity. 

Immobilizing DENs within a sol-gel matrix is another potential method for preparing new supported catalysts. PAMAM and PPI dendrimers can be added to sol-gel preparations of silicas " and zinc arsenates to template mesopores. In one early report, the dendrimer bound Cu + ions were added to sol-gel silica and calcined to yield supported copper oxide nanoparticles. Sol-gel chemistry can also be used to prepare titania supported Pd, Au, and Pd-Au nanoparticle catalysts. Aqueous solutions of Pd and Au DENs were added to titanium isopropoxide to coprecipitate the DENs with Ti02. Activation at 500°C resulted in particles approximately 4 nm in diameter. In this preparation, the PAMAM dendrimers served two roles, templating both nanoparticles and the pores of the titania support. 

Fig. 3 Results for the photocatalytic reduction of nitrate in the presence of 0.04 M HCOOH as hole scavenger over titania and Ag/Ti02 catalysts prepared by impregnation (IMP) or photodeposition (Photo) and comparing use of Degussa P25 (49 m g ) with Hombikat UV 100 (250 m g ) as supports. ...

Supported Palladium. - For catalysts prepared by impregnation with PdQ2 on silica, titania, and alumina supports and reduced (673 K), the width of the Pd 3c 5/2 lines in the photoelectron spectra was greater than the value for unsupported palladium and decreased in the order... 

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