Alloy precursors

Some examples of ternary alloy precursors are also shown. Their general properties were examined and their microstructures were directly observed by transmission electron microscopy. Thus, catalysts synthesized from multi-system alloys had high solubility of additional elements into a major element, and might be expected to work as new catalysts. 

Alloy Precursors Solvent Stabilizer position ( C) Size (mn) References... 

Fig.l Temperature dependence of the conversion of carbon dioxide on the catalysts prepared from amorphous Ni-40Zr and Ni-(40-x)Zr-xSm alloy precursors. 

Fig.4 Change in the relative peak height of 111 reflection for the tetragonal zirconia in the catalysts prepared from the amorphous alloy precursors as a function of nickel content in the catalysts.

In this context, rare earths on transition metal substrates attracted considerable research attention from two directions i) to understand the overlayer growth mechanisms involved [3] and ii) to prepare oxide-supported metal catalysts from bimetallic alloy precursor compounds grown in situ on the surface of a specific substrate [4,5]. The later studies are especially significant in terms of understanding the chemistry and catalytic properties of rare earth systems which are increasingly used in methanol synthesis, ammonia synthesis etc. In this paper, we shall examine the mechanism of Sm overlayer and alloy formation with Ru and their chemisorption properties using CO as a probe molecule. 

Alloy precursor Methanol activity11 Maximum (mole kg-1 h ) Steady state Activation energy (kJ mole 1) Surface area (m2 g )... 

The SEL approach has some advantages over co-deposition, because it allows simpler coulometric control of the precursor stoichiometry. The SEL method may also be more suitable for large-scale fabrication since there is no requirement to balance the deposition rates of several different metals, so higher current densities can be used. If an alloyed precursor is preferred for the sulfur annealing step, a short (<5min) heat treatment at 200-350 °C is sufficient to completely alloy the stacked precursor. In this section, we highlight some of our recent work on the fabrication of CZTS solar cells by the SEL route [11]. 

Here, we present a computational study on Raney-Nickel [1], which is a nanostructured amorphous catalyst used in many industrial applications. It is routinely used in hydrogenation reactions such as the reduction of benzene to cyclohexane. Raney-Nickel is typically prepared by quenching a molten mixture of a NiAl alloy from which Al is leached out for producing the final catalyst The initial alloy precursor composition is important because it affects the NiAl phases formed during the quenching process. These phases have different leaching properties influencing the porosity of the catalyst and thus its performance. 

The synthesis of dealloyed PtCus catalyst involved the preparation of PtCus precursor alloys at the first step, which was followed by electrochemical dissolution of Cu (dealloying). PtCus alloy precursors were prepared by a conventional... 

Fig. 18.5 (a) ORR voltammetry in 02-saturated 0.1 M HCIO4 of dealloyed PtCu3 catalysts using the alloy precursors annealed at 600, 800, and 950 compared to a commercial Pt catalyst. (Inset) CV curves of the dealloyed PtCu3 catalysts in N2 saturated 0.1 M HCIO4. (b) Comparison of Pt-mass activities at 0.9 V/RHE. (c) Comparison of Pt-area-specific activities at 0.9 V/RHE (reprint with permission from ref. [27])... 

To investigate the possible lattice-strain mechanism on the enhanced ORR activities, we synthesized two sets of dealloyed Pti xCnx catalysts from a wide range of alloy precursor compositions (Pt3Cu, ftCu, and PtCu3) one set was annealed at 800 °C and the other set annealed at 950 °C [43]. The idea is that the composition of the alloy core determines the upper limit of the strain on the Pt shell and thus enables a lattice-strain control, which is crucial for the study of strain-activity relationships. 

Snyder J, Asanithi P, Dalton AB, Erlebacher J (2008) Stabilized nanoporous metals by dealloying ternary alloy precursors. Adv Mater 20(24) 4883 886... 

Figure IS Schematic representation of the formation of a Pt-enriched core-shell alloy nanoparticle by voltammet-ric dealloying of a Cu-rich alloy precursor (Pt, gray Cu. red Co, blue). Reproduced with permission from [25] copyright Wiley-VCH Verlag GmbH, Co. KGaA.

Inoue and Kimura (Inoue Kimura, 2000) have summarized the microstructure and mechanical properties of aluminum based alloys produced by controlling the crystallization of amorphous alloy precursors, as shown in Fig. 10. A high mechanical strength exceeding... 

Finally, the all-important effect of the presence of the bifunctional structural promoters will be demonstrated. They promote both formation and stabilization of the metastable, active form of a-iron. This form has been found to be exactly the same in the technical catalyst and in a model catalyst system prepared from amorphous alloy precursors.In Fig. 2.48 conversion measurements are shown for a set of catalysts made from the same iron oxide starting material, but which contained different promoter additives. All three catalysts were activated in the same way, according to the manufacturer s specification. 

Hydrolysis and polycondensation reactions usually occur simultaneously and the reaction rates depend on the type of precursor as well as on reaction conditions such as pH, temperature, and ionic strength [8]. Hydrolysis of alkoxy precursors (=M-OR , where M is the metal atom and R is the alkyl group) occurs by water due to electrophilic reaction in the presence of acid catalyst or by nucleophilic substitution of alkoxy groups in the presence of base catalyst [3,9]. The hydrolyzed precursors (=M-OH) can react either with alloy precursors (alcoxolation) or with other hydrolyzed precursors (oxolation). In both cases the mechanism is nucleophilic substitution or nucleophilic addition for which the result is polycondensation [3,10]. The reactions that describe the sol-gel process are as follows ... 

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