Synergetic catalytic effects

Co ions show the strongest catalytic effect whereas Cu, Fe and Mn, frequently accused of being degradation catalysts, are not always so, and Pb and Zn are not always inert as might be expected. Synergetic and antagonistic effects may appear in commercial polymers which generally contain traces of a variety of metals. 

Recently, however, the development of nanotechnology may provide the changes on the research and development of practical catalysts. As mentioned in the previous section we can now design and synthesize a metal nanoparticle with not only various sizes and shapes, but also with various combinations of elements and their locations. Thus, we can now design the synergetic effect of two elements. In the case of core/shell structured bimetallic nanoparticles, the shell element can provide a catalytic site and the core element can give an electronic effect (a ligand effect) on the shell element. Since only the atoms on the surface can be attached by substrates, the thickness of the shell should be an important factor to control the catalytic performance. 

The flexibility in composition of LDHs has led to an increase in interest in these materials. As a result of their relative ease of synthesis, LDHs represent an inexpensive, versatile and potentially recyclable source of a variety of catalyst supports, catalyst precursors or actual catalysts. In particular, mixed metal oxides obtained by controlled thermal decomposition of LDHs have large speciflc surface areas (100-300 m /g), basic properties, a homogeneous and thermally stable dispersion of the metal ion components, synergetic effects between the elements, and the possibility of structure reconstruction under mild conditions. In this section, attention is focused on recently reported catalytic applications in some flelds of high industrial and scientific relevance (including organic chemistry, environmental catalysis and natural gas conversion). 

From a true catalytic point of view, what is looked for are so-called synergetic effects , i.e., a reciprocal influence between two or more components so as to obtain a material whose activity exceeds that of the pure components [74]. This usually involves intimate electronic interaction between the various components so that their electronic structures become profoundly modified. It is well possible that a metal deprived of part of its valence electrons may behave as the element on its left in the Periodic Table [75]. However, the theory of synergetic effects is still in its infancy in electrochemistry. Predictions for a bimetallic catalyst with two non-interacting sites obtained by combining two metals with different adsorption energies are that... 

So far, the atomistic modeling on oxidation of CO and methanol has been aimed to elucidate mechanisms for (1) the bifunctional effect, in which the unique catalytic properties of each of the elements in the alloy combine in a synergetic fashion to yield a more active surface and (2) the ligand or electronic effect, in which the interaction between dissimilar atoms yield alters electronic states and hence results in a more active catalytic surface. In parallel to the study on the OER, study of oxidation of CO and methanol has seen a progress from vapor phase models to liquid phase models. However, polymer cluster has not been involved in the ab initio models. 

Catalytic activity in zeolitic materials is strongly influenced by the type of alkali metal cations, and maximum catalytic activity, e.g, in isomerization reactions, is explained by the formation of an imide species EuNH [305]. Synergetic effects were observed in bimetallic supported Si02 which showed considerable hydrogen uptake during hydrogenation reactions [307]. The formation of Ln-NH2, -NH, -N species seemed to be suppressed in the presence of transition metal powders and precipitation of elemental lanthanides is favored [309]. Lanthanide imides were favored as active species in the Ln/AC-mediated cyclization of ethyne and propyne [310]. 

Heterogeneous layers based on semiconducting metal oxides are known to show gas-sensing features different as compared to single oxides [1,2], The mentioned synergetic phenomenon can be provided by two effects i) the presence of active centers with diverse adsorption and catalytic behavior ii) the efficient separation of the sensor functions, receptor and transducer, between different oxide phases. 

The results of the catalytic tests clearly indicate the existence of a cooperation between M0O3 and BiP04. The fact that synergetic effects were observed both for the conversion of isobutene and for the selectivity to methacrolein suggests that there has been creation of new selective sites during the reaction. 

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