Catalysts, general solid

By 19884 it became obvious that the NEMCA effect, this large apparent violation of Faraday s law, is a general phenomenon not limited to a few oxidation reactions on Ag. Of key importance in understanding NEMCA came the observation that NEMCA is accompanied by potential-controlled variation in the catalyst work function.6 Its importance was soon recognized by leading electrochemists, surface scientists and catalysis researchers. Today the NEMCA effect has been studied already for more than 60 catalytic systems and does not seem to be limited to any specific type of catalytic reaction, metal catalyst or solid electrolyte, particularly in view of... 

The selective deposition technique seems a surface modification of oxides. In this regard, the modification of material surface is generally carried out in the field of the catalyst preparation. Catalysts are divided into heterogeneous and homogeneous catalysts. The former is well known to be used in the petroleum industry and almost all catalysts are solid, in particular, the supported catalysts. The supported catalysts are composed of the main... 

The concept is general and one-pot acid/base and enzyme/catalyst enantioselective solid-state syntheses are easily achieved by entrapment of the mutually destructive reagents in two different sol-gel silicas. It is worth pointing out that while acids and bases adsorbed at the surface of polymers are left partly exposed and consequently require acid/base solid-state... 

Solid acidic oxide catalysts generally do not show intrinsic acidity comparable with liquid superacids, and therefore generally high temperatures are required to achieve catalytic activity. 

With the aid of metallocene catalysts, plastics can be made for the first time with a property profile that is precisely controllable and within wide limits. This precise control of properties such as temperature resistance, hardness, impact strength, and transparency had not been possible until recently because conventional Ziegler-Natta catalysts are generally solids on the surfaces of which relatively nonuniform catalytic action takes place. The nonuniformity of the surfaces results in corresponding nonuniformity in the resulting polymers. 

A catalyst preparation step. The catalysts, which are generally solids, are produced with the careful exclusion of water and oxygen. 

Tn is the bulk melting temperature, 7 and p are the surface energy and the density of the solid phase and the liquid phase noted by the subscripts s and 1 and L is the latent heat of fusion. This phenomenon is due to the increase in the fraction of surface atoms. The Pawlow law is verified experimentally for particles larger than 5 nm and more sophisticated thermodynamic models have been developed which can be applied down to 2-nm particles [54]. During catal 4ic reactions, particles are generally solid, but in the case of carbon nanotubes synthesized by CVD, the catalyst particles could melt at temperatures lower than the bulk melting point. 

The question arises, why do bi- or multi-phasic catalysts generally show better activity and selectivity than the active phase alone The aim of this paper is to answer this question by exploring the role of interfacial effects. We shall examine first how the thermodynamic and structural properties of one phase influence its interactions, not only with the gaseous reactants, but also with coexisting solid phases as a result of its bulk, surface, and defect structure. We will also examine the conditions necessary for these interactions and set up a structural classification of the main components of mild oxidation catalysts. This will lead finally to a discussion of the role of interfacial effects in catalyst performance using some illustrative examples. Thermodynamic and Structural Properties of Single Phase Catalysts... 

In contrast to these specific compounds, most catalysts are solid oxides or sulfides possessing high surface areas, generally 50-500 mVg- Some catalysts contain finely divided constituents in metallic form deposited on the surface of a support. 

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