Catalytic potential

Materials that show significant ammonia synthesis activity can be divided into three categories according to their ability to form nitrides  

2) Metals forming nitrides unstable under reaction conditions (Mn, Fe, Co, Ni. Te, Re) 

3) Metals likely to be present as nitrides under synthesis conditions (groups 3-6 of 

Of the platinum group metals only ruthenium and osmium show an activity superior to iron, though only in presence of alkali metal promoters, as may be seen from Table 20 [386], 

The group of metals forming low-stability or unstable nitrides includes Mn, Fe, Co, Ni, Tc and Re. As in the case of iron a clear structural sensitivity was found for rhenium but the role of promoters remains the subject of discussion. There are also indications of structure sensitivity for cobalt and nickel. It was attempted to improve the activity of the classical magnetite catalyst by alloying with nickel or cobalt. The only commercial catalyst is a cobalt containing magnetite [392], 

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The enhanced binding predicts a catalytic potential for these solutions and prompted us to investigate the influence of the different types of micelles on the rate of the copper-ion catalysed reaction. Table 5.5 summarises the results, which are in perfect agreement with the conclusions drawn from the complexation studies. 

First of all, given the well recognised promoting effects of Lewis-acids and of aqueous solvents on Diels-Alder reactions, we wanted to know if these two effects could be combined. If this would be possible, dramatic improvements of rate and endo-exo selectivity were envisaged Studies on the Diels-Alder reaction of a dienophile, specifically designed for this purpose are described in Chapter 2. It is demonstrated that Lewis-acid catalysis in an aqueous medium is indeed feasible and, as anticipated, can result in impressive enhancements of both rate and endo-exo selectivity. However, the influences of the Lewis-acid catalyst and the aqueous medium are not fully additive. It seems as if water diminishes the catalytic potential of Lewis acids just as coordination of a Lewis acid diminishes the beneficial effects of water. Still, overall, the rate of the catalysed reaction... 

A considerable number of EDTA complexes of ruthenium have been synthesized [130-132] there has been interest in their catalytic potential while several compounds have had their structures determined. Synthetic routes relating to these compounds are shown in Figure 1.50. 

These examples are part of a broader design scheme to combine catalytic metal complexes with a protein as chiral scaffold to obtain a hybrid catalyst combining the catalytic potential of the metal complex with the enantioselectivity and evolvability of the protein host [11]. One of the first examples of such systems combined a biotinylated rhodium complex with avidin to obtain an enantioselective hydrogenation catalyst [28]. Most significantly, it has been shovm that mutation-based improvements of enantioselectivity are possible in these hybrid catalysts as for enzymes (Figure 3.7) [29]. 

The wide choice of new methods for the synthesis of P-chirogenic phosphines can be appreciated from the above results,. The synthetic description of this chapter ends here and gives place to the great catalytic potential of these ligands. 

Another SBU with open metal sites is the tri-p-oxo carboxylate cluster (see Section 4.2.2 and Figure 4.2). The tri-p-oxo Fe " clusters in MIL-100 are able to catalyze Friedel-Crafts benzylation reactions [44]. The tri-p-oxo Cr " clusters of MIL-101 are active for the cyanosilylation of benzaldehyde. This reaction is a popular test reaction in the MOF Hterature as a probe for catalytic activity an example has already been given above for [Cu3(BTC)2] [15]. In fact, the very first demonstration of the catalytic potential of MOFs had aheady been given in 1994 for a two-dimensional Cd bipyridine lattice that catalyzes the cyanosilylation of aldehydes [56]. A continuation of this work in 2004 for reactions with imines showed that the hydrophobic surroundings of the framework enhance the reaction in comparison with homogeneous Cd(pyridine) complexes [57]. The activity of MIL-lOl(Cr) is much higher than that of the Cd lattices, but in subsequent reaction rans the activity decreases [58]. A MOF with two different types of open Mn sites with pores of 7 and 10 A catalyzes the cyanosilylation of aromatic aldehydes and ketones with a remarkable reactant shape selectivity. This MOF also catalyzes the more demanding Mukaiyama-aldol reaction [59]. 

Except for exploring its catalytic potential, CHMO from Acinetobacter has also been used as a model system for upscaling BVMO-mediated biocatalysis. 

KDHRF A homologous restriction factor binds to C8 65KDHRF A homologous restriction factor, also known as C8 binding protein interferes with cell membrane pore-formation by C5b-C8 complex Kcat Catalytic constant a measure of the catalytic potential of an enzyme Ka Equilibrium dissociation constant kD Kilodalton Kd Dissociation constant KD Kallidin... 

Important inherent characteristics of an enzyme that should be considered are the substrate affinity, characterized by the Michaelis constant the rate of turnover fecat> providing the catalytic efficiency fecat/ M. and the catalytic potential. Several attempts to compare enzyme catalysis with that of platinum have been published. Direct comparisons are difficult, because enzyme electrodes must be operated in aqueous electrolyte containing dissolved substrate, whereas precious metal electrodes aie often supplied with a humidified gaseous stream of fuel or oxidant, and produce water as steam. It is not straightforward to compare tme optimal turnover rates per active site, as it is often unclear how many active sites are being engaged in a film of enzyme on an electrode. 

The results clearly show that these novel ligands are able to form a suitable asymmetric enviromnent around the metal resulting in high asymmetric induction. Their catalytic potential has been demonstrated in the highly enantioselective Rh-catalyzed hydrogenation of itaconates and a-enamides and Ru-catalyzed hydrogenation of p-functionalized ketone. 

Our future work towards the investigation of the catalytic potential of our novel catalysts will involve more inert substrates such as aryl chlorides and bromides. 

In view of catalytic potential applications, there is a need for a convenient means of characterization of the porosity of new catalyst materials in order to quickly target the potential industrial catalytic applications of the studied catalysts. The use of model test reactions is a characterization tool of first choice, since this method has been very successful with zeolites where it precisely reflects shape-selectivity effects imposed by the porous structure of tested materials. Adsorption of probe molecules is another attractive approach. Both types of approaches will be presented in this work. The methodology developed in this work on zeolites Beta, USY and silica-alumina may be appropriate for determination of accessible mesoporosity in other types of dealuminated zeolites as well as in hierarchical materials presenting combinations of various types of pores. 

The abundance of accessible donor and acceptor orbitals in common transition-metal complexes facilitates low-energy bond rearrangements such as insertion ( oxidative-addition ) reactions, thus enabling the critically important catalytic potential of metals. 

We emphasize that the above results have been observed only in the oxidation of sulfides and phenols, reactions known to follow radical mechanisms. A thorough investigation of the catalytic potential of the materials in other oxidation reactions (epoxidation, hydroxylations, etc.) is warranted. 

Up to now the main interest in these compounds has been their structural characterization there is still much to be learned about their methods of synthesis, their chemical reactivity and their catalytic potential. 

This study suggests that interlayer spacing and molecular size of contaminant may be important in determining the catalytic potential of minerals in the environment. 

A. Scott, A. Dianat, F. Borrnert, A. Bachmatiuk, S. Zhang, J.H. Warner, et al., The catalytic potential of high-K dielectrics for graphene formation, Applied Physics Letters, 98 (2011) 073110. 

It is unlikely that the terrorists who, in July 2005, attempted to cause explosions on the London Underground by using a mixture of hydrogen peroxide and flour, obtained the idea of this explosive mixture from a knowledge of the biology of the Bombardier beetle. The mixture failed to explode through failure of the detonators. The secretion of enzymes with their enormous catalytic potential ensures no such failure in the beetle. 

Polyoxometalates undoubtedly have enormous catalytic potential in liquid phase selective oxidation of organic compounds. Various strategies for immobilization of POMs on solid matrices have been developed during the past two decades and opened new opportunities for practical applications. The most developed and widely used technique is electrostatic... 

Tsogoeva and co-workers explored the catalytic potential of pyridyl- and imida-zoyl-containing thiourea derivatives (e.g., thiourea 92 and 93) in the asymmetric model Strecker reactions [157] of N-benzyl- and benzhydryl-protected benzaldi-mine with HCN [258], The observed enantioselectivities were consistently very low (4—14% ee) for all catalyst candidates and were far below synthetically useful levels, while imidazoyl-thiourea 93 was reported to be highly active and displayed 100% conversion (at 7% ee) of the N-benzhydryl-protected benzaldimine (Scheme 6.99). X-ray structure analysis of a pyridyl-thiourea revealed an intramolecular hydrogen-bond between the basic ring nitrogen and one amide proton. This could make this... 

Overall, therefore, activation of the thrombolytic cascade occurs exactly where it is needed— on the surface of the clot. This is important as the substrate specificity of plasmin is poor, and circulating plasmin displays the catalytic potential to proteolyse fibrinogen, factor V and factor VIII. Although soluble serum tPA displays a much reduced activity towards plasminogen, some free circulating plasmin is produced by this reaction. If uncontrolled, this could increase the risk of subsequent haemorrhage. This scenario is usually averted, as circulating plasmin is rapidly... 

The catalytic potential of the MTO/UHP oxidation system has also been tested in the room-temperature ionic liquid [EMIM] [BF4], in which it is soluble [77]. In contrast, the olefin is poorly soluble in such solvenfs. Therefore, the whole system is biphasic. Excellent conversions and selectivities for the epoxides of a wide number of olefinic substrates were reached under these anhydrous conditions. The exception was 1-decene (data collected in Table 17), for which poor conversion (entry 9, Table 17) may result in phase transfer problems, since it is the least soluble substrate in the ionic liquid. 

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