EFFECT ON CATALYTIC PROPERTIES

Valkirs, A. (1978). Temperature and pH effects on catalytic properties of lactate dehydrogenase from pelagic fish. Comparative Biochemistry and Physiology 59A, 31-36. 

Lambert reviews the role of alkali additives on metal films and nanoparticles in electrochemical and chemical behavior modihcations. Metal-support interactions is the subject of the chapter by Arico and coauthors for applications in low temperature fuel cell electrocatalysts, and Haruta and Tsubota look at the structure and size effect of supported noble metal catalysts in low temperature CO oxidation. Promotion of catalytic activity and the importance of spillover are discussed by Vayenas and coworkers in a very interesting chapter, followed by Verykios s examination of support effects and catalytic performance of nanoparticles. In situ infrared spectroscopy studies of platinum group metals at the electrode-electrolyte interface are reviewed by Sun. Watanabe discusses the design of electrocatalysts for fuel cells, and Coq and Figueras address the question of particle size and support effects on catalytic properties of metallic and bimetallic catalysts. 

Solid state chemistry plays an important role in the catalysis by Transition Metal Sulfides however, it is a role that is somewhat different than the role usually assigned to solid state chemistry in catalysis. In catalysis, by sulfides, the chemistry of ternary phases is not now important and thus, the usual role of solid state chemistry in preparing ternary phases and systematically studying the effect on catalytic properties through variation of the composition of these ternary phases is absent. Nevertheless, preparation of the Transition Metal Sulfides is crucial in controlling the properties of the catalysts. Low temperature solid state preparations are the key to obtaining good catalysts in reasonable surface area for catalytic measurements. 

The third metalic (M) components were added into the colloidal silica and the mixture were dried up and calcined. The obtained dry gels were impregnated again with a CsOH solution. Then, the catalyst was calcined again at 400 °C. The Cs/M/Si atomic ratio was 20/10/1000. TTie effects on catalytic properties were studied in the reaction of MP with formalin in the presence of methanol. The amoimt of propylene formed by the dehydration of of 2-propanol was measured at 200 °C, as an index of the amount of acidic sites on the surface. 

From this short survey, it should become clear that metal alkoxide, beside their working considerations, have very large prospective applicability in different area of organic reaction catalysis which must be investigate more comprehensively to show their properties more clearly. Steric and electronic possessions have crucial effect on catalytic properties of metal alkoxides like many other metal complexes. In one hand, electronic properties of different substituents on alkyl R group of metal alkoxides determine their metal core Lewis acidic property and/or Lewis basic character of alkoxy oxygen atom which both have substantial effect on their catalytic behavior. In addition, steric properties of alkyl R group may hinder substrate to come closer or to attack by active site of catalyst. 

Porosity Effects on Catalytic Properties Naturai, Periodic, and imprinted Porosities 967... 

As previously reported, physicochemical characteristics of catalysts prepared from undoped or Cu-doped alloys were rather similar. For both samples, / -crystallizationcauses a similar effect reduction of total and metallic surface areas (15-20%) and an increase of the A1 content (20-30%). From Auger and XPS analyses, Cu was found in a metallic state and seemed substituted at random in the Ni lattice. The same effect on catalytic properties by /(-crystallization of the precursor alloy, observed with the undoped and Cu-doped catalysts, could be explained by the similarity of the microstructure of both types of samples. 

The effect that the presence of hydrogen in the lattice of nickel or nickel-copper alloys has on catalytic properties is much more difficult to trace in the literature than is the case with palladium and its alloys. Several factors contribute to this ... 

O.A. Mar ina, V.A. Sobyanin, V.D. Belyaev, and V.N. Parmon, The effect of electrochemical oxygen pumping on catalytic properties of Ag and Au electrodes at gas-phase oxidation ofCH4, Catalysis Today 13, 567-570 (1992). 

Effect of oxidative treatments on catalytic property of carbon nanofiber composite... 

For adequate reaction rates, a high concentration of iodide anion is necessary. The cation portion of the salt appears to have little or no effect on catalytic activity or reaction selectivity. Inorganic iodides (such as potassium iodide) are the obvious first choice based on availability and cost. Unfortunately these catalysts have very poor solubility in the reaction mixture without added solubilizers or polar, aprotic solvents. These solubilizers (e.g., crown ethers) and solvents are not compatible with the desired catalyst recovery system using an alkane solvent. Quaternary onium iodides however combine the best properties of solubility and reactivity. 

Despite numerous screening studies, the literature contains little evidence that homogeneous catalyst systems based on metals other than Co, Rh, or Ru have significant activity for catalytic CO reduction. As seen for the known active catalytic systems, however, properties of solvents and additives or promoters can have enormous effects on catalytic activities. Solvents and additives can serve many roles in these catalytic systems. One important function of promoters in the Rh and Ru systems appears to be that of stabilizing metal oxidation states involved in catalytic chemistry. Other... 

A wide variety of solid surfaces is used as catalysts in an even wider assortment of industrial processes (see, for example, Richardson 1989 and Somorjai 1994) we limit our discussion to metal catalysts. While these represent only a fraction of all catalytic systems, they do include a number of industrially important examples. Table 9.6 lists some metals used as commercial catalysts and indicates briefly the types of reactions for which they are employed. In this section we emphasize the effect on catalytic activity of the chemical and crystallographic properties of metal surfaces. 

The modification of the Ni Al alloy by addition of molybdenum or chromium has a significant effect on the properties of the Raney nickel catalyst in the reaction of hydrogenation of valeronitrile. In the case of molybdenum, the catalytic properties may be correlated to the physico-chemical characteristics of the catalysts. Chromium is an effective promoter for initial activity and for selectivity. The mechanism for promotion of chromium in Raney nickel is not known exactly. 

The experimental results described in this review support the concept that, in certain reactions of the redox type, the interaction between catalysts and supports and its effect on catalytic activity are determined by the electronic properties of metals and semiconductors, taking into account the electronic effects in the boundary layer. In particular, it has been shown that electronic effects on the activity of the catalysts, as expressed by changes of activation energies, are much larger for inverse mixed catalysts (semiconductors supported and/or promoted by metals) than for the more conventional and widely used normal mixed catalysts (metals promoted by semiconductors). The effects are in the order of a few electron volts with inverse systems as opposed to a few tenths of an electron volt with normal systems. This difference is readily understandable in terms of the different magnitude of, and impacts on electron concentrations in metals versus semiconductors. 

The foregoing sections have been concerned with the effect of particle size on the structure and properties of small metal particles. Several general comments can be made concerning the influence of particle size on catalytic properties. 

The conclusion is that particle size effects on catalytic activity or selectivity due to variations in the inherent properties of small metal particles (geometric or electronic) are unlikely to be important for particles larger than about 1.5-2.0 nm. If size effects are observed for larger particles it is necessary to consider the nature and origin of such effects. 

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