Catalysis surface specificity

The measurement of heats of adsorption by means of microcalorimetry has been used extensively in heterogeneous catalysis in the past few decades to gain more insight into the nature of gas-surface interactions and the catalytic properties of solid surfaces. Specific attention will be focused on group IIIA containing samples in this section. 

An effective approach to help address the issues involved in controlling catalyst performance is to formulate and analyze reaction schemes that describe the essential chemistry taking place on the catalyst surface. This approach has been used successfully in catalysis research for many years. We suggest that this approach will see increased use in catalysis research. Specifically, continuing improvements in computer capabilities allow rapid analysis of complex reaction schemes for all common reactor configurations (e.g., reactors operating at steady state as well as under transient reaction conditions and nonisothermal reactors). Moreover, recent advances in quantum... 

For more than two decades, extensive research work has been devoted to the unique properties of clusters. They are made of a small number (or nucleaiity) of atoms or molecules only, and therefore constitute a new state of matter, or mesoscopic phase, between the atom or molecule and the crystal. New methods have been developed in physics and chemistry for their synthesis, their direct observation, the study of their properties, and of their crucial role in number of processes, such as phase transition, catalysis, surface phenomena, imaging. Owii to its specific approach, radiation chemistry offei first the opportunity to reveal the existence of nuclearity-dependent properties of clusters and has then proven to be a powerfid method to study the mechanisms of cluster formation and reactivity in solution. 

The solid/gas interface was traditionally studied with respect to adsorption and catalysis. Here the assertion that the Bronsted definition of acidity is a particular case of the Lewis definition is neither obvious nor even helpful. It suffices to say that many reactions in heterogeneous catalysis require specifically the presence of either Bronsted or Lewis acidic (or basic) sites, and the reaction mechanisms depend on the nature of the surface site. A long-term goal of surface studies for the characterization of solid catalysts was to distinguish and quantify the number of Bronsted or Lewis sites with potential catalytic activity for gas-phase reactants. For that reason, when discussing the acid-base behavior of solid surfaces, it is no longer possible, nor desirable, to adopt the viewpoint that subsumes Bronsted acid-base properties in the more general Lewis definition. 

Amorphous silica gels exhibit a large diversity in structural properties. To be used as a supporting agent in heterogeneous catalysis, high specific surface and high stability is necessary. Moreover, for many applications in selective catalysis a tailor-made porous structure is necessary or very desirable. 

The extremely high surface specificity of ISS is important in many areas of application, including heterogeneous catalysis and growth of semiconductor surfaces because the nature of the outermost atomic layers determines the... 

The typical industrial catalyst has both microscopic and macroscopic regions with different compositions and stmctures the surfaces of industrial catalysts are much more complex than those of the single crystals of metal investigated in ultrahigh vacuum experiments. Because surfaces of industrial catalysts are very difficult to characterize precisely and catalytic properties are sensitive to small stmctural details, it is usually not possible to identify the specific combinations of atoms on a surface, called catalytic sites or active sites, that are responsible for catalysis. Experiments with catalyst poisons, substances that bond strongly with catalyst surfaces and deactivate them, have shown that the catalytic sites are usually a small fraction of the catalyst surface. Most models of catalytic sites rest on rather shaky foundations. 

Of these, the most extensive use is to identify adsorbed molecules and molecular intermediates on metal single-crystal surfaces. On these well-defined surfaces, a wealth of information can be gained about adlayers, including the nature of the surface chemical bond, molecular structural determination and geometrical orientation, evidence for surface-site specificity, and lateral (adsorbate-adsorbate) interactions. Adsorption and reaction processes in model studies relevant to heterogeneous catalysis, materials science, electrochemistry, and microelectronics device failure and fabrication have been studied by this technique. 

Transition state theory, 46,208 Transmission factor, 42,44-46,45 Triosephosphate isomerase, 210 Trypsin, 170. See also Trypsin enzyme family active site of, 181 activity of, steric effects on, 210 potential surfaces for, 180 Ser 195-His 57 proton transfer in, 146, 147 specificity of, 171 transition state of, 226 Trypsin enzyme family, catalysis of amide hydrolysis, 170-171. See also Chymotrypsin Elastase Thrombin Trypsin Plasmin Tryptophan, structure of, 110... 

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... 

Proteins derive their powerful and diverse capacity for molecular recognition and catalysis from their ability to fold into defined secondary and tertiary structures and display specific functional groups at precise locations in space. Functional protein domains are typically 50-200 residues in length and utilize a specific sequence of side chains to encode folded structures that have a compact hydrophobic core and a hydrophilic surface. Mimicry of protein structure and function by non-natural ohgomers such as peptoids wiU not only require the synthesis of >50mers with a variety of side chains, but wiU also require these non-natural sequences to adopt, in water, tertiary structures that are rich in secondary structure. 

Characterization of catalytic phenomena at oxide surfaces includes (1) characterization of established catalyst surfaces to improve the catalytic performance, (2) characterization of new catalysts in comparison with conventional catalysts, (3) characterization of specific model surfaces such as single crystals and epitaxial flat surfaces to transfer the knowledge so obtained to catalytic systems or even to create a new type of catalyst, and (4) characterization of catalysis... 

Supported iron catalysts are notoriously difficult to reduce [6-8] and thus a substantial fraction of the iron can be expected to remain inactive for the catalysis of hydrogenation. Particular attention has therefore been paid to the preparation of Fe/MgO catalysts by several different methods and examination of their effectiveness in producing metallic iron of adequate specific surface area after reduction in hydrogen. The activity and selectivity for primary amine formation have been determined for the hydrogenation of ethanenitrile (acetonitrile) and propanenitrile. 

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