Metal-support interactions mechanism

An important question frequently raised in electrochemical promotion studies is the following How thick can a porous metal-electrode deposited on a solid electrolyte be in order to maintain the electrochemical promotion (NEMCA) effect The same type of analysis is applicable regarding the size of nanoparticle catalysts supported on commercial supports such as Zr02, Ti02, YSZ, Ce02 and doped Zr02 or Ti02. What is the maximum allowable size of supported metal catalyst nanoparticles in order for the above NEMCA-type metal-support interaction mechanism to be fully operative ... 

Confirmation of the Self-driven NEMCA Metal-Support Interaction Mechanism... 

The good qualitative agreement between eUwR variation and O0 variation shown in Figure 11.11 for the various supports used, underlines again the common promotional mechanism of electrochemically promoted and metal-support interaction promoted metal catalysts. 

Maleic acid hydrogenation, 481 Metal-support interactions and electrochemical promotion, 490 and electrophobic reactions, 499 mechanism of, 490 model for, 507 Metcalfe, modeling, 316 Methanation, electrochemical promotion of, 406, 409... 

In situ ETEM permits direct probing of particle sintering mechanisms and the effect of gas environments on supported metal-particle catalysts under reaction conditions. Here we present some examples of metals supported on non-wetting or irreducible ceramic supports, such as alumina and silica. The experiments are important in understanding metal-support interactions on irreducibe ceramics. 

The concept of mechanical fixation of metal on carbon makes catalytic applications at high temperatures possible. These applications require medium-sized active particles because particles below 2nm in size are not sufficiently stabilised by mechanical fixation and do not survive the high temperature treatment required by the selective etching. Typical reactions which have been studied in detail are ammonia synthesis [195, 201-203] and CO hydrogenation [204-207]. The idea that the inert carbon support could remove all problems associated with the reactivity of products with acid sites on oxides was tested, with the hope that a thermally wellconducting catalyst lacking strong-metal support interactions, as on oxide supports, would result. 

In conclusion, even if the CH3OH oxidation occurs for supported electrocatalysts in a similar way as on smooth Pt electrodes, the surface characteristics of the catalysts, besides Pt dispersion, may play a significant role in the reduction of the overpotential for this process. The acid-base functional groups influence the oxidation mechanism as they establish the level of metal-support interaction and the surface adsorption behavior. Thus, the optimization of such parameters can significantly improve the activity of Pt electrocatalysts for CH3OH oxidation. 

Promotion and metal-support interactions play a key role in the design of successful commercial finely dispersed nanoparticle catalysts [1-5]. The detailed molecular mechanism of promotion [6] and particularly of metal-support interactions [7,8] is still a subject of intensive study and dispute. 

The goal of this chapter is to summarize and systematize the phenomenology of the three phenomena, i.e., classical promotion, electrochemical promotion, and metal-support interactions, present their striking similarities and some common rules that govern them, and demonstrate their intimate link and common molecular mechanism. 

It was only the use of larger metal particles deposited on these supports, up to 1 pm in size, comparable to the spatial resolution of XPS, that enabled researchers to understand the origin of electrochemical promotion and, at the same time, to discover the backspillover mechanism of metal-support interactions [137,138]. 

Thus on the basis of the experiments of Cavalca et al. [141], in conjunction with the XPS studies surveyed previously, it is reasonable to anticipate that the mechanism of metal-support interaction promotion of catalytic oxidations is the same with the mechanism of self-driven electrochemical promotion systems self-induced migration of promoting species on the nanoparticle catalysts... 

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