Catalyst preparation decomposition deposition

The use of highly dispersed catalysts from soluble salts of molybdenum is another approach to the reduction of catalyst amount because of their excellent activity despite their higher price. Recently, metal carbonyl compounds, such as Fe(CO)5, Ru3(CO)i2, and Mo(CO)6 have been investigated as metal cluster catalysts. Preparation involved their deposition and decomposition on catalyst support surfaces (71-73). 

Berthet, A., Thomann, A. L., Aires, F. J. C. S., Brun, M., Deranlot, G, Bertolini, J. C., Rozenbaum, J. P., Brault, P., and Andrezza, P., Comparison of bulk Pd/(Bulk SiC) catalysts prepared by atomic beam deposition and plasma sputtering decomposition Characterization and catalytic properties. J. Catal. 190, 49 (2000). 

The above procedures for catalyst preparation have generally provided excellent results. Especially important are surface-sensitive reactions. With supported catalysts in which the active components have a narrow particle-size distnbution, the optimum particle size for a demanding reaction can be established. Major improvements of supported catalysts, e.g. with respect to carbon deposition and ammonia decomposition, can be achieved by preparing catalysts with a narrow par-ticle-size distribution. Also, the preparation of catalysts in which the active components have a uniform chemical composition is highly important One instance is the preparation of supported vanadium oxide phosphorus oxide (VPO) catalysts for the selective oxidation of w-butane to maleic anhydride, which has been carried out using vanadium(III) deposition onto silica [31]... 

Lee S, Fan CY, Wu TP, Anderson SL (2005) Hydrazine decomposition over Ir /Al O model catalysts prepared by size-selected cluster deposition. J Phys Chem B 109 381... 

Supported model catalysts are prepared by deposition of atoms, under UHV, on a clean, well-ordered oxide surface. We do not review other preparation methods based on wet impregnation [5] and decomposition of metal-organic complexes [9], which are close to industrial methods but less subject to investigation by surface-... 

The previous examples are all supported gold catalysts. Supported bimetallic catalysts have been explored as well. Scurrell and coworkers developed a series of Au-M/ Fe Oj (M=Ag, Bi, Co, Cu, Mn, Ni, Pb, Ru, Sn, Tl) catalysts for WGS [70,71], These catalysts were prepared by deposition-coprecipitation using HAuCl, FeCNOjjj, and metal salts as precursors, followed by calcination in air at 400°C. Au-Ru/Fe Oj showed the highest activity. However, there is no evidence showing that the so-called bimetallic catalysts are bimetallic. The thermal decomposition of metal salts in air usually leads to the formation of metal oxides instead [61]. 

The quartz made fluidized-bed reactor used for catalyst preparation was electrically heated a cyclone was incorporated into the freeboard of the reactor to prevent elutriation of fines. The support, which was fluidized by N2 was first thermally pretreated to remove physisorbed water. Then the vaporized metal acetyl acetonate was adsorbed on the support at 400 K at constant partial pressure in a flow of N2 for a ven period of time. The subsequent decomposition of the adsorbate was carried out by increasing the fluidized-bed temperature with a rate of 4 K/min. Pt was deposited in either N2 or air at 573 K Cr203 and V2O5 were deposited in air at 673 K. Pt catalysts which were decomposed in N2 were additionally treated in air at 573 K (Pt/Si02 catalysts) respectively at 773 K (Pt/Al203 catalysts) [4, 5]. 

Metal acetyl acetonate decomposition on alumina goes along with the formation of carbonaceous surface compounds Pt particles which were deposited in N2 are masked by adsorbed CO. Furthermore, detectable amounts of carbon are deposited on the catalyst surface when decomposing the adsorbed metal acetyl acetonate in N2 [4, 5]. The contaminations are removable by an additional air treatment of the samples as applied in catalyst preparation (see above). 

In fhe cafalysf preparation, not only the choice of the active phase precursor is cra-cial, the method of catalyst preparation is decisive, too, for obtaining good dispersion of the active phase. Active phase can be deposited on supports by impregnation, ion-exchange, adsorption, etc. Once selected the nature of support and active phase, the observed differences in dispersion should only be due to the method of preparation. Dispersed iron oxide catalysts (FeOx) have received much attention because their potentiality for many applications in environmental catalysis (N2O decomposition and reduction) and in fine chemical industry (Friedel-Crafts, isomerisations, etc.). For most applications, high dispersion of the metal centres is desirable to enhance the activity-selectivity pattern of the catalysts. 

Multi-component noble metal catalysts prepared by sequential deposition precipitation for low temperature decomposition of dioxin, M. Okumura, T. Akita, M. Haruta, X. Wang, O. Kajikawa, and O. Okada, Appl. Catal. B, 2003, 41,43. 

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... 

With nickel/alumina catalysts (cf. 4 ) preparation by coprecipitation or by the decomposition of a high dispersion of nickel hydroxide on fresh alumina hydrogel, yields nickel aluminate exclusively. On the other hand, when, as in impregnation, larger particles of nickel compound are deposited, the calcination product is a mixture of nickel oxide and nickel aluminate. The proportion of nickel oxide increases when occlusion of the impregnation solution leads to a very nonuniform distribution (49). 

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