Catalyst bifunctional

The azinones and their reaction characteristics are discussed in some detail in Section II, E. Because of their dual electrophilic-nucleophilic nature, the azinones may be bifunctional catalysts in their own formation (cf. discussion of autocatalysis below) or act as catalysts for the desired reaction from which they arise as byproducts. The uniquely effective catalysis of nucleophilic substitution of azines has been noted for 2-pyridone. 

The catalytic effect of protons, of bifunctional catalysts, and of base is demonstrated in the amination of chloro derivatives of pyridazine, pyrimidine, and s-triazine (Tables V and VI). Anilino-s-triazines containing NH groups act as catalysts in their own formation. The catalytic action of protons on anhino-dechlorination of 2-chloro-4,6-diamino-s-triazine and of 2-amino-4-chloropyrimidine was reported in the classic paper by Banks. ... 

Benzyne 72, 184ff., see also Aryne Bifunctional catalysts 361 Bilirubin, in azo coupling 323 f. 

Bifunctional catalysis in nucleophilic aromatic substitution was first observed by Bitter and Zollinger34, who studied the reaction of cyanuric chloride with aniline in benzene. This reaction was not accelerated by phenols or y-pyridone but was catalyzed by triethylamine and pyridine and by bifunctional catalysts such as a-pyridone and carboxylic acids. The carboxylic acids did not function as purely electrophilic reagents, since there was no relationship between catalytic efficiency and acid strength, acetic acid being more effective than chloracetic acid, which in turn was a more efficient catalyst than trichloroacetic acid. For catalysis by the carboxylic acids Bitter and Zollinger proposed the transition state depicted by H. 

The process of direct synthesis of DME includes reactions of methanol synthesis and methanol dehydration, which are catalyzed by two different catalysts. Although the technology for the production of methanol is generally considered mature, most of thran are gas phase process, and the performances of these catalysts are restricted remarkably in liquid phase process. Development of high performance bifunctional catalyst system is very... 

Scheme 9 Examples of ligand-metal bifunctional catalysts...

To illustrate how a bifunctional catalyst operates, we discuss the kinetic scheme of the isomerization of pentane [R.A. van Santen and J.W. Niemantsverdriet, Chemical Kinetics and Catalysis (1995), Plenum, New York]. The first step is the dehydrogenation of the alkane on the metal ... 

We have explored rare earth oxide-modified amorphous silica-aluminas as "permanent" intermediate strength acids used as supports for bifunctional catalysts. The addition of well dispersed weakly basic rare earth oxides "titrates" the stronger acid sites of amorphous silica-alumina and lowers the acid strength to the level shown by halided aluminas. Physical and chemical probes, as well as model olefin and paraffin isomerization reactions show that acid strength can be adjusted close to that of chlorided and fluorided aluminas. Metal activity is inhibited relative to halided alumina catalysts, which limits the direct metal-catalyzed dehydrocyclization reactions during paraffin reforming but does not interfere with hydroisomerization reactions. 

Bifunctional Catalysts. The adatoms provide suitable adsorption sites for a second reactant necessary for the reaction to proceed, while the main reactant still adsorbs on the free sites of the substrate. 

A bifunctional catalyst should be able to activate two different reaction steps (methanol and water adsorption and surface reaction between adsorbed species), and so active sites with different properties are necessary. As an example, investigations of possibihty of enhancing activity with regard to methanol electro-oxidation with Pt-Ru-based electrodes are of great interest with regard to improving the electrical efficiency of DMFCs. Several approaches have been considered the effect of Pt-Ru... 

Castagnola, M.J., Neylon, M.K. and Marshall, C.L. (2004) Coated bifunctional catalysts for NOx SCR with C3H6 Part II. In situ spectroscopic characterization, Catal. Today, 96, 61. 

Flame Processes—Theoretical and Experimental J. F. Wehner Bifunctional Catalysts J. H. Sinfelt... 

Whatever the mechanistic explanation for this remarkable result, we hope that we have given the reader a taste of the fruits of considering both the fields of enzyme mechanism and organometallic chemistry. We are exploring the acceleration of other reactions using bifunctional catalysts, and these results will be described in due course. 

The metallic component of HCK catalysts provides hydrogenation, dehydrogenation, hydrogenolysis, and isomerization. The number and nature of reactive hydrogen species created by the interaction of a bifunctional catalyst with hydrogen is not well understood [103], on the other hand, neither the action of those species on the catalytic sites is understood. The main limitation in this understanding is the dynamic character of the interaction however, now that in situ characterization techniques are becoming available, research would soon defeat the limitations. 

The classical HCK mechanism on bifunctional catalysts separates the metallic action from that of the acid by assigning the metallic function to the creation of an olefin from paraffin and the isomerization and cracking of the olefins to the acid function. Both reactions are occurring through carbenium ions [102],... 

Three approaches of solution of the reaction (13) catalyst problem are used application of bifunctional catalysts, two catalysts in one layer and two catalysts in two layers. 

As it follows from Table 5, many catalysts contain metallic platinum. We have developed bi-layer porous hydrophobic air electrodes, which do not contain platinum metals, are active and can be cycled [24, 25] (Figures 4-6). These bifunctional catalysts are pyrolized Co - macrocyclic compounds. Said catalyst has high catalytic activity for the oxygen reduction and also features acceptable stability, however its activity for the oxygen evolution is not high enough. 

Hydroisomerization of n-hexadecane on Pt/HBEA bifunctional catalysts effect of the zeolite crystallites size on the reaction scheme. 

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