Bimetallic catalysts pathways

In core- (and focal point-) functionalized dendrimers, the catalyst can especially benefit from the specific microenvironment created by dendritic structures. Site-isolation effects can be beneficial for reactions that are deactivated by excess ligand, and can also prevent bimetallic deactivation pathways. 

How the hypothetical reaction pathway represented by Eqs. (1) to (3) may be accomphshed in a real bimetallic alloy nanoparticle Recently, Bard and co-workers discussed the possibihty to completely remove Pt from the alloy systems and proposed thermodynamic guidehnes for the design of bimetallic catalysts for dioxygen elecfroieduction. Furthermore, Wang and Balbuena... 

DFT has been extremely useful in predicting that a Cu/Ag bimetallic catalyst would be more selective than Ag alone. However, the validity of the method of using DFT calculations of a reaction pathway on Agis clusters as a model for fhe real cafalysf which would be surface oxidised under reaction conditions is... 

The weakness of our dicationic bimetallic catalyst is the fact that it readily fragments in acetone or other polar organic solvents into inactive monometallic (12r) and double-P4 coordinated bimetallic (13rr) complexes. The proposed firag-mentation pathway is shown in Fig. 9 and starts with the dissociation of one of the external phosphine chelate arms. 

Abstract Direct formic acid fuel cells offer an alternative power source for portable power devices. They are currently limited by unsustainable anode catalyst activity, due to accumulation of reaction intermediate surface poisons. Advanced electrocatalysts are sought to exclusively promote the direct dehydrogenation pathway. Combination and structure of bimetallic catalysts have been found to enhance the direct pathway by either an electronic or steric mechanism that promotes formic acid adsorption to the catalyst surface in the CH-down orientation. Catalyst supports have been shown to favorably impact activity through either enhanced dispersion, electronic, or atomic structure effects. 

The discovery of this bimetallic pathway has led to the design of tethered metal-salen dimers and oligomers 48 and 49. These catalyst systems have been found to exhibit higher catalytic activity, both in terms of yields and ee s, than their monomeric counterparts 50 and 51, which provides further evidence for the proposed cooperative bimolecular pathway. 

The PtRu bimetallic system has been the catalyst of choice for MeOH oxidation in acid elecfrolyfes since its discovery by workers at Shell in the early 1960s2 In practice, PtRu lowers the overpotential for MeOH oxidation by >200 mV compared to pure Pt. The MeOH oxidation reaction on Pt and PtRu is probably the most studied reaction in fuel cell electrocatalysis due to its ease of sfudy in liquid electrolytes and the many possible mechanistic pathways. In recent years, the deposition of PtRu particles onto novel carbon supports and the novel PtRu particle preparation routes have proved popular as a means to demonstrate superiority over conventional PtRu catalysts. 

For example, Table 7.3 shows the comparison of half-wave potential, and the number of electrons transferred for the O2 reduction in acidic solution at Au—Pt/C bimetallic nanoparticles of various compositions, measured by RDE technique. It can be clearly seen that a 4-electron-transfer pathway is mainly operative for ORR and the half-wave potential for ORR on bimetallic Au—Pt/C (20% 20%) is lOO mV less negative when compared with that of Pt/C (home-made and E-Tek). Au—Pt/C (30 10) shows a negative shift in a half-wave potential in comparison with both Pt/C samples, indicating that the catalytic activity decreases with increasing Au content. It is believed that an optimum content of Au will contribute to a reduction in the Pt-OH formation that is known to poison the catalyst for ORR. 

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