Catalysts, hydrogenation active site

If two such types of site having different catalytic abilities coexist on a catalyst surface, the isomerization and hydrogenation reactions of olefins could proceed simultaneously but on different sites. As will be discussed later, it is rather reasonable that real catalysts involve active sites with different abilities. For this reason, the Horiuti and Polanyi mechanism which assumes a priori common alkyl intermediates for the isomerization and hydrogenation reactions, appears less logical. 

Pradier et al. (81) do not confirm the results obtained in the hydrogenation of butadiene on Pt(l 10) when they consider the (100) face. The activity decrease is no longer proportional to the sulfur coverage. They consider that the sulfur action changes with the crystallographic face the sulfur would adsorb on the diene sites over the (100) face, but on the hydrogen activation sites, over the (110) face. Moreover, the complexity of the sulfur action is not only seen by changing the substrate or the catalyst. It is... 

The catalytic activity of a powder catalyst should be proportional to its surface area in case its entire surface is equally effectii-e for the catalytic reaction. On the other hand, this correlation does not apply to catalysts whose active sites are located at crystallographically exceptional positions such as edges and corners of its microcrystallies. Schwab and Rudoloph (99) studied as early as 1934 the Topochemistry in Heterogeneous Catalysis, and concluded that the active sites of several catalysts were located at crystal boundaries in their surfaces. The chief evidence represented by these workers is that in various catalytic reactions, e.g., in the hydrogenation of ethyl cinnamate over different specimens of powdered nickel catalysts, the rates are proportional to a power of the catalyst surface areas lying between 1.8 and 4.0. 

Naphthalene and its derivatives are one of the more dominant aromatics present in various diesel and jet fuel feedstocks. Therefore, several investigators have reported the influence of naphthalene on HDS of model compounds. One of the first reports was by Lo who found naphthalene to weakly inhibit the conversion and selectivity of the HDS of DBT. Similarly, LaVopa and Satterfield found little effect of naphthalene and phenanthrene on the HDS of thiophene. Other researchers have, however, found naphthalene to be a stronger inhibitor of HDS activ-ity. Nagai and Kabe, in fact, found naphthalene to significantly reduce catalyst selectivity for the hydrogenation pathway.Isoda et al., on the basis of similar selectivity inhibition, concluded that naphthalene severely inhibits the hydrogenation active sites in a... 

It is assumed that the water gas shift activity is related to the alkalized oxidic part of the iron catalyst. Hydrogen - activated on the oxidic sites - could support the hydrogenation of earbon on the earbidie sites [11] to form the CH2 monomer . 

Catalyst activity. An increase in catalyst activity will increase della coke. As catalyst activity increases so does the number of adjaceni sites, which increases the tendency for hydrogen transfer reactions to occur. Hydrogen transfer reactions are bimolecular and require adjacent active sites. 

The much more stable MIL-lOO(Cr) lattice can also be impregnated with Pd(acac)2 via incipient wetness impregnation the loaded catalyst is active for the hydrogenation of styrene and the hydrogenation of acetylene and acetylene-ethene mixtures to ethane [58]. MIL-lOl(Cr) has been loaded with Pd using a complex multistep procedure involving an addition of ethylene diamine on the open Cr sites of the framework. The Pd-loaded MIL-lOl(Cr) is an active heterogeneous Heck catalyst for the reaction of acrylic acid with iodobenzene [73]. 

AXB) shows time courees of amounts of evolved hydrogen and decalin conversions with caibon-supported platinum-based catalysts unda" supeiheated liquid-film conditions. Enhancement of dehydrogenation activities for decalin was realized by using fiiese composite catalysts. The Pt-W / C composite catalyst exhibited the hipest reaction rate at the initial stage, whereas the Pt-Re / C composite catalyst showed the second highest reaction rate in addition to low in sensitivity to retardation due to naphthaloie adsorbed on catalytic active sites [1-5], as indicated in Fig. 2(A) ). 

The performance of various solvents can be explained with the help of the role of these solvents in the reaction. These solvents help in keeping teth benzene and hydrogen peroxide in one phase. This helps in the easy transport of both the reactants to the active sites of the catalyst. The acetonitrile, and acetone adsorption data on these catalysts (Fig. 6), suggests that acetonitrile has a greater affinity to the catalytic surface than acetone. There by acetonitrile is more effective in transporting the reactants to the catalyst active sites. At the same time, they also help the products in desorbing and vacating the active sites. 

Enzymes are nature s catalysts. For the moment it is sufficient to consider an enzyme as a large protein, the structure of which results in a very shape-specific active site (Fig. 1.3). Flaving shapes that are optimally suited to guide reactant molecules (usually referred to as substrates) in the optimum configuration for reaction, enzymes are highly specific and efficient catalysts. For example, the enzyme catalase catalyzes the decomposition of hydrogen peroxide into water and oxygen... 

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