Bimetallic catalysts synthesis

Table 3.4 Selective metal partitioning for bimetallic catalyst synthesis.

Jacobsen CJH, Dahl S, Clausen BS, Bahn S, Logadottir A, Nprskov JK. 2001. Catalyst design by interpolation in the periodic table bimetallic ammonia synthesis catalysts. J Am Chem Soc 123 8404-8405. 

Besides direct reduction, a one-pot reductive amination of aldehydes and ketones with a-picoline-borane in methanol, in water, and in neat conditions gives the corresponding amine products (Scheme 8.2).40 The synthesis of primary amines can be performed via the reductive amination of the corresponding carbonyl compounds with aqueous ammonia with soluble Rh-catalyst (Eq. 8.17).41 Up to an 86% yield and a 97% selectivity for benzylamines were obtained for the reaction of various benzaldehydes. The use of a bimetallic catalyst based on Rh/Ir is preferable for aliphatic aldehydes. 

Bahome, M. C., Jewell, K., Padayachy, L. L., Padayachy, K., Hildebrandt, D., Glasser, D., Datye, A. K., and Coville, N. J. 2007. Fe-Ru small particle bimetallic catalysts supported on carbon nano tubes for use in Fischer-Tropsch synthesis. Applied Catalysis A General 328 243-51. 

Ffirai and Toshima have published several reports on the synthesis of transition-metal nanoparticles by alcoholic reduction of metal salts in the presence of a polymer such as polyvinylalcohol (PVA) or polyvinylpyrrolidone (PVP). This simple and reproducible process can be applied for the preparation of monometallic [32, 33] or bimetallic [34—39] nanoparticles. In this series of articles, the nanoparticles are characterized by different techniques such as transmission electronic microscopy (TEM), UV-visible spectroscopy, electron diffraction (EDX), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) or extended X-ray absorption fine structure (EXAFS, bimetallic systems). The great majority of the particles have a uniform size between 1 and 3 nm. These nanomaterials are efficient catalysts for olefin or diene hydrogenation under mild conditions (30°C, Ph2 = 1 bar)- In the case of bimetallic catalysts, the catalytic activity was seen to depend on their metal composition, and this may also have an influence on the selectivity of the partial hydrogenation of dienes. 

The SEA method can also be applied for the synthesis of bimetallic catalysts. For illustration, the potentially high impact area of bimetallic catalysts for fuel cells will be discussed. 

Another useful bimetallic for fuel cell electrodes is Pt/Ru. Ruthenium is readily oxidized to Ru02 by calcination after it is impregnated. The PZC of ruthenium oxide is unknown. Propose a comprehensive sequence of experiments with which the SEA method can be applied for the synthesis of a Pt/Ru bimetallic catalyst supported on carbon. The goal is to have intimate contact between the Pt and Ru phases in the final, reduced catalyst. 

Synthesis of Supported Bimetallic Catalysts from Molecular Cluster Precursors... 

In CO hydrogenation, the achvity and selechvity to C1-C5 oxygenates over the bimetallic samples are higher than those of the monometallic counterparts [187-190]. Bimetallic catalysts also showed improved activity in the hydroformylation of ethylene compared to either of the monometallic catalysts [191]. The promotion for higher alcohol production is proposed to be associated with the adjacent Ru-Co sites. However, the lack of an exhaustive characterization of catalysts does not allow a clear correlation to be established between the characteristics of the active sites and the catalytic behavior. A formyl species bonded to a Ru-Co bimetallic site has been proposed to be the intermediate in the alcohol synthesis in these systems. A subsequent reaction with an alkyl-surface group would lead to the C2-oxygenate production [187]. 

In support of the conclusion based on silver, series of 0.2, 0.5, 1.0, 2.0, and 5.0 % w/w of platinum, iridium, and Pt-Ir bimetallic catalysts were prepared on alumina by the HTAD process. XRD analysis of these materials showed no reflections for the metals or their oxides. These data suggest that compositions of this type may be generally useful for the preparation of metal supported oxidation catalysts where dispersion and dispersion maintenance is important. That the metal component is accessible for catalysis was demonstrated by the observation that they were all facile dehydrogenation catalysts for methylcyclohexane, without hydrogenolysis. It is speculated that the aerosol technique may permit the direct, general synthesis of bimetallic, alloy catalysts not otherwise possible to synthesize. This is due to the fact that the precursors are ideal solutions and the synthesis time is around 3 seconds in the heated zone. 

Chandler BD, Gilbertson JD (2006) Dendrimer-Encapsulated Bimetallic Nanoparticles Synthesis, Characterization, and Applications to Homogeneous and Heterogeneous Catalysis. 20 97-120 ChataniN (2004) Selective Carbonylations with Ruthenium Catalysts. 11 173-195 Chatani N, see Kakiuchi F (2004) 11 45-79... 

Table 8-3 Synthesis of hydrogen peroxide comparison of palladium, gold and bimetallic catalyst.123...

Rates of deactivation of Ni and Ni bimetallic catalysts as a result of poisoning by 10-ppm H2S during methanation were investigated in a series of studies by Bartholomew and co-workers (23, 113, 161, 194). Effects of catalyst composition and geometry, gas composition and reaction temperature on the rate of deactivation were considered. Deactivation rates were found to be relatively insensitive to temperature and quite sensitive to gas and catalyst composition (194). In fact, the rates of deactivation were 2-3 times more rapid in a H2-rich mixture (H2 /CO = 99), compared to a normal synthesis (H2/CO = 3-4) mixture. 

We have reported on a tandem procedure for the synthesis of 3-allyl-N-(alkoxycarbonyl)indoles 115 via the reaction of 2-(alkynyl)phenylisocyanates 114 and allyl carbonates 5 in the presence of Pd(PPh3)4 (lmol%) and CuCl (4 mol%) bimetallic catalyst [80]. A proposed mechanism is shown in Scheme 35. Initially, the insertion of the isocyanates 114 into the complex 7, formed by the reaction of 5 with Pd(0), would form the 7r-allylpalladium intermediates 117. This intermediate, with Pd - N bonding, could be in equilibrium with the Pd - O bonded intermediates 118, which should more probably be represented as the bis-7r-allylpalladium analogue 119. Insertion of the alkyne then occurs to form the indoles 115 and the Pd(0) species is regenerated. It should be emphasized that no carboamination takes place at all in the absence of CuCl the product 116 was obtained. 

The d-f heteronuclear or lanthanide-transition metal (abbreviated as Ln-M) complexes attract interest from both academic and industry because of the challenge for their synthesis, the novelty of their structures, and their potential application as advanced materials, such as molecular or nano magnets,bimetallic catalysts, and sensors. The complexes can be assigned to three categories based on the nature of the Ln-M interaction (a) complexes with direct Ln-M bonding, (b) complexes with Ln-M interactions bridged by ligands, and (c) the complexes with ionically associated Ln-coordination units and M-coordination units. Most of the d-f heteronuclear complexes of carboxylic acids reported so far are found with type (b) structure, and very few of them are of structure type (c). The lanthanides and the transition metals in these complexes are far away from each other, and no direct Ln-M interactions have been observed. 

Bimetallic catalysts, Ru/Rh [15-17] and Ru/Re [18], were found to be effective for the selective synthesis of ethylene glycol. A bimetallic Ru/Co catalyst gives ethanol [19], while Ru/Mn and Ru/Ti give methanol [20], In the presence of ammonia, syngas can be converted into the corresponding formamide with the Ru3(CO)i2/Bu4PBr catalyst (Eq. 11.5) [21]. 

The calibration and application of a heat flux DSC in the study of heterogeneous reactions has been discussed in the literature (248). The possibilities and limitations of this technique were demonstrated for methanation and methanol synthesis on Cu/ZnO catalysts. More recently, Rejai and Gonzalez (222, 223) used a DSC to investigate the reduction of Pt02, PtCl2, and H2PtCl6, the decomposition of calcium oxalate, and the formation of supported Pt-Ru bimetallic catalysts. The results were consistent with values based on standard enthalpies of formation reported in the literature. This work illustrates the power of calorimetry for studying the important processes involved in catalyst preparation and treatment. 

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