Electrochemically-prepared bimetallics, metal

Electrochemical Synthesis of Bimetallic Particles. Most chemical methods for the preparation of metal nanoparticles are based at first on the reduction of the corresponding metal ions with chemical reagents to form metal atoms and then on the controlled aggregation of the obtained metal atoms. Instead of chemical reduction, an electrochemical process can be used to create metal atoms from bulk metal. Reetz and Hclbig proposed an electrochemical method including both oxidation of bulk... 

The metatheis of acetates with the alkali alkoxides (method 5) can be used for the preparation of the methoxides and ethoxides of all three elements and is the only reaction leading to Hg(OR)2 [1623]. The trans-esterification of Zn(OMe)2 (method 6), according to [1121], can be carried out only in the presence of LiOR (forming soluble bimetallic complexes). The direct electrochemical synthesis on the anodic oxidation of metals in alcohols has been described for Zn(OEt)2 and a series of cadmium derivatives (Cd(OR)2 — obtained in the presence of such donor ligands as Dipy, Phen, and Dmso [98]) (method 2). 

The cryptand (33) containing three ferrocene redox centers (78) has been prepared by our group via the synthetic pathway shown in Scheme 13. Although electrochemically insensitive to Group IA metal cations, this cryptand does electrochemically recognize Zn2+ and forms an isola-ble 2Zn2t (33) bimetallic complex. 

Bimetallic catalysts can be prepared by a direct redox method when a cationic complex of a metal of higher electrochemical potential is reduced by another metal of lower electrochemical potential that has been deposited and reduced first187 (see Table 4.10) PdAu/SiO 88 and PdAu/C189 have been made in this way, gold being deposited after the palladium. Small amounts of the metals were found in filtrates, and XRD and temperature-programmed decomposition of palladium hydride indicated a substantial... 

In practice the preparation of bimetallic catalysts using direct redox reactions can be extensively used for depositing a noble metal with a high standard electrochemical potential onto a non-noble metal with a lower standard electrochemical potential (eq 3). 

In summary, the direct redox reactions can be largely used in the preparation of bimetallic catalysts with a close interaction between the metallic constituents. In that case a metal with a high electrochemical potential is deposited on a metal with a lower potential. The applicability of the technique can be extended significantly by using different ligands which, by chelating metallic ions, modify the standard electrochemical potentials. 

In summary, the preparation of bimetallic catalysts by surface redox reaction using a reductant preadsorbed on the parent monometallic catalyst has been studied in detail. Unfortunately, the method is intricate and time consuming, especially if several successive operations are required. Furthermore, when the modifier has a standard electrochemical potential higher than that of the parent metal (AUCI4 deposited on Pt°), the overall reaction is a complex one involving a reduction by adsorbed reductant but also direct oxidation of the metallic parent catalyst. The relative rate of the two parallel reactions determines the catalytic properties of the resulting bimetallic catalyst. 

In bimetallic catalysts prepared by catalytic reduction of copper by hydrogen, copper is deposited as three-dimensional agglomerates which are located, at low copper loadings, on the edges, corners, and rims of the parent metallic particles. The mechanism of deposition can be transferred from that proposed in corrosion and involving a local electrochemical cell ... 

In heterogeneous catalysis, the first tests on UPD were performed on bulk catalysts which allows, for the preparation of the bimetallic catalyst, easy control of the electrochemical potential by an external device (potentiostat). In the same way all electrochemical techniques, particularly the control of catalyst potential required for submonolayer deposition, can be extrapolated to metallic catalysts supported on conductive materials such as carbon or carbides [8]. 

The preparation of bimetallic surfaces can be performed by physical, chemical, and electrochemical methods depending on the proportions of both the metals that are used. Electrodeposition methods are advantageous because of their simplicity and selectivity, as it is possible to screen rapidly the different... 

Methods of Controlled Surface Reactions (CSRs) and Surface Organometallic Chemistry (SOMC) were developed with the aim to obtain surface species with Sn-Pt interaction. In CSRs two approaches have been used (i) electrochemical, and (ii) organometallic. Characteristic feature of the organometallic approach is that both CSR and SOMC results in almost exclusively supported alloy type bimetallic nanoclusters. Studies on the reactivity of tin organic compounds towards hydrogen adsorbed on different transition and noble metals have revealed new aspects for the preparation of supported bimetallic catalysts. 

Nitrate electroreduction has been extensively studied over the last few decades. This reactitMi is a multi-electron transfer process showing different mechanisms as a function of pH, nitrate and supporting electrolyte concentration, chemical composition and structure of the catalyst. In recent years, nitrate electroreduction has been widely studied over diamond and many monometallic electrodes such as Pb, Ni, Zn or Rh, Ru, Ir, Pd, Cu, Ag and Au. Because none of the common pure metals is able to provide high selectivities for nitrogen, bimetallic alloys or monometals modified with foreign metal adatoms were prepared and evaluated for the reduction of nitrate. More recently, an electrochemical process in which nitrate ions are reduced to ammonia at the cathode, and where the produced ammonia is oxidized at the anode to nitrogen with the contribution of hypochlorite ions, has been evaluated. 

In an electrochemical way of making metal nanopartides, a solution of stabilizer e.g., tetraalkylammonium bromide in THF) is electrolyzed using an anode made of the metal of interest and an inert cathode.l Under the conditions of the electrolysis, dissolution of the anode material takes place via oxidation. The metal cations transfer to the cathode, where reduction, nucleation and finally stabilization occur. The size of thus-prepared nanopartides can be easily controlled by the current density. The method is applicable to many transition metals. Moreover, systems with two anodes of different metals result in the formation of bimetallic nanopartides. When oxidation of the anode metal is difficult, the metal of interest can be introduced as inorganic salt.h67] pd nanopartides, e.g., prepared via this method were found to be catalyticaUy active in the Heck reaction and the... 

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