Preparation reduction-deposition

Bio-ethanol is attracting growing interests in relation to the shift of raw materials from petroleum to biomass. A pioneering work by Christensen is that over MgAl203 support gold is much more selective to acetic acid than palladium and platinum in the aerobic oxidation of ethanol in water in a batch reactor. Figure 32 shows that selectivity to acetic acid exceeds 80% [99]. In contrast, Au/Si02 catalysts prepared by deposition reduction... 

The catalysts were prepared by deposition of Pd nanoparticles on the CFl, CF2, CF3, and CF4 resins respectively, shown in Figure 5, by chemical reduction of Pd(II) precursors such as Pd(OAc)2 and PdCl2(NCR)2 (R = Ph, Me), following the CIR procedure, or by deposition from Pd-solvated atoms obtained via MVS. 

Carbon-supported platinum (Pt) and platinum-rathenium (Pt-Ru) alloy are one of the most popular electrocatalysts in polymer electrolyte fuel cells (PEFC). Pt supported on electrically conducting carbons, preferably carbon black, is being increasingly used as an electrocatalyst in fuel cell applications (Parker et al., 2004). Carbon-supported Pt could be prepared at loadings as high as 70 wt.% without a noticeable increase of particle size. Unsupported and carbon-supported nanoparticle Pt-Ru, ,t m catalysts prepared using the surface reductive deposition... 

In Ni/Al203 catalysts prepared by impregnation there is a weaker interaction between the impregnating salt and the support than there is when the catalyst is prepared by deposition-precipitation. Calcination of the former catalysts gave large nickel oxide crystallites and, on reduction, the supported metal was rather easily sintered. Catalysts prepared by precipitation-deposition, on the other hand, were resistant to sintering because of the strong interaction... 

Model Ni/MnOx catalysts have been prepared by deposition of 150 of Ni onto an oxidized Mn disk. Subsequent reduction at 500 K in ul-trahigh vacuum results in rapid segregation of MnO onto the Ni surface. The segregation rate is ouch faster than that of Ti under identical conditions. HREELS studies reveal new C-0 stretching bands at lower frequencies, comparable to what have been observed on Rh promoted with Mn. We assign these bands to be due to CO chemisorbed on or near MnO sites. 

Cobalt porphyrins and phthalocyanines were used as precursors for preparation of carbon supported cobalt catalysts that displayed high activity in reduction of oxygen in fuel cells [9-12], These samples were prepared by deposition of cobalt phtalocyanine on active carbon following by heat treatment at 650-700°C in an inert atmosphere providing formation of Co-N structure deposited on active carbon. 

Electrodeposition is the preferred method for preparing a thin, smooth, uniform, and stable source for counting, as discussed in Section 3.7. Empirically developed procedures are applied to the heavy elements in aqueous solution because they cannot be reduced to the metal the source is deposited at the cathode in what is believed to be hydroxy forms after partial reduction. Deposition is in acid solution, under various conditions that yield near-quantitative recovery from the solution. Test results specify the volume, reagent content, applied volts and amperes, and optimum time period (see Section 6.4.1). The cathode can be a platinum disk, but a polished stainless steel disk is satisfactory. 

Recently, Soria et al. [109] also investigated the effect of synthesis method on the WGS activity of Au/Fc203 catalysts. They prepared catalysts by deposition-precipitation method, liquid phase reductive depositions and double impregnation method. Among the various catalysts, the catalyst synthesized by deposition-precipitation method exhibits higher CO conversion. 

Galvanic displacement method is also often used for synthesizing catalysts. By this method, low Pt-content electrocatalysts can be obtained. For example, a carbon-supported core—shell structured electrocatalyst with bimetallic IrNi as the core and platinum monolayer as the shell has been successfully synthesized using this method. In this synthesis, IrNi core supported on carbon was first synthesized by a chemical reduction and thermal annealing method and a Ni core and Ir shell structure could be formed finally. The other advantage of this method is that the Ni can be completely encased by Ir shell, which will protect Ni dissolve in acid medium. Secondly, IrNi PtML/C core—shell electrocatalyst was prepared by depositing a Pt monolayer on the IrNi substrate by galvanic displacement of a Cu monolayer formed by under potential deposition (UPD). 

One of the major challenges to understanding bimetallic catalysts is to obtain supported clusters with relatively well understood and uniform compositions. Supported bimetallic catalysts are usually prepared by deposition of metal salts onto a support followed by caldnation and reduction by H2 at elevated temperature. lliis approach leads to nonuniformities in cluster composition and structure and even physical separation of the two metals. These difficulties have prompted research on catalysts prepared from molecular metal clusters since they provide precursors of well defined stoichiometry and structure. 

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