Activation of the metal

With special techniques for the activation of the metal—e.g. for removal of the oxide layer, and the preparation of finely dispersed metal—the scope of the Refor-matsky reaction has been broadened, and yields have been markedly improved." The attempted activation of zinc by treatment with iodine or dibromomethane, or washing with dilute hydrochloric acid prior to use, often is only moderately successful. Much more effective is the use of special alloys—e.g. zinc-copper couple, or the reduction of zinc halides using potassium (the so-called Rieke procedure ) or potassium graphite. The application of ultrasound has also been reported. ... 

The CF and GF represent the coke- and gas-forming tendencies of an E-cat compared to a standard steam-aged catalyst sample at the same conversion. The CF and GF are influenced by the type of fresh catalyst and the level of metals deposited on the E-cat. Both the coke and gas factors can be indicative of the dehydrogenation activity of the metals on the catalyst. The addition of amorphous alumina to the catalyst will tend to increase the nonselective cracking, which forms coke and gas. 

Pourbaix has evaluated all possible equilibria between a metal M and HjO (see Table 1.7) and has consolidated the data into a single potential-pH diagram, which provides a pictorial summary of the anions and cations (nature and activity) and solid oxides (hydroxides, hydrated oxides and oxides) that are at equilibrium at any given pH and potential a similar approach has been adopted for certain M-H2O-X systems where A" is a non-metal, e.g. Cr, CN , CO, SOj , POj", etc. at a defined concentration. These diagrams give the activities of the metal cations and anions at any specified E and pH, and in order to define corrosion in terms of an equilibrium activity, Pourbaix has selected the arbitrary value of 10 ° g ion/1, i.e. corrosion of a metal is defined in terms of the pH and potential that give an equilibrium activity of metal cations or anions > 10 g ion/1 conversely, passivity and immunity are defined in terms of an equilibrium activity of < 10 g ion/1. (Note that g ion/1 is used here because this is the unit used by Pourbaix in the S.I, the relative activity is dimensionless.)... 

In 1965, Breslow and Chipman discovered that zinc or nickel ion complexes of (E)-2-pyridinecarbaldehyde oxime (5) are remarkably active catalyst for the hydrolysis of 8-acetoxyquinoline 5-sulfonate l2). Some years later, Sigman and Jorgensen showed that the zinc ion complex of N-(2-hydroxyethyl)ethylenediamine (3) is very active in the transesterification from p-nitrophenyl picolinate (7)13). In the latter case, noteworthy is a change of the reaction mode at the aminolysis in the absence of zinc ion to the alcoholysis in the presence of zinc ion. Thus, the zinc ion in the complex greatly enhances the nucleophilic activity of the hydroxy group of 3. In search for more powerful complexes for the release of p-nitrophenol from 7, we examined the activities of the metal ion complexes of ligand 2-72 14,15). 

One way of overcoming the liquid junction potential problem is to replace the reference electrode by an electrode composed of a solution containing the same cation as in the solution under test, but at a known concentration, together with a rod of the same metal as that used in the indicator electrode in other words we set up a concentration cell (Section 2.29). The activity of the metal ion in the solution under test is given by... 

The screened proton model of nickel or palladium hydrides and Switendick s concept of the electronic structure do not constitute a single approach sufficient to explain the observed facts. In this review, however, such a model will be used as the basis for further discussions. It allows for the explanation and general interpretation of the observed change of catalytic activity of the metals, when transformed into their respective hydrides. 

The para-hydrogen conversion catalytic activity of the metals belonging to the first transition series Ti, V, Cr, Mn, Fe, Co, Ni was compared by Eley and Shooter (70). The purpose of the research was not to discover... 

At high alkali coverages (near monolayer coverage), when the adsorbed alkali overlayer shows a metal-like character, alkali-methoxy species are formed. As shown by TPD experiments in the system K/Ru(001) these alkali-methoxy species are more stable than the methoxy species on clean Ru(001) and adsorbed methanol on 0.1K/Ru(001). On metal surfaces inactive for methanol decomposition, e.g. Cu(lll), these alkali-methoxy species are formed even at low alkali coverages, due to the weaker interaction of the alkali atoms with the metal surface. The formation of these species stabilizes the methoxy species on the metal surface and enhances the activity of the metal surface for methanol decomposition. 

Again the extent to which such parallel reactions contribute to the measured current is not very easy to quantify. However, fortunately, such a quantification is not necessary for the description of NEMCA. What is needed is only a measure of the overall electrocatalytic activity of the metal-solid electrolyte interface or, equivalently, of the tpb, and this can be obtained by determining the value of a single electrochemical parameter, the exchange current I0, which is related to the exchange current density i0 via ... 

More sophisticated materials have been made by attachment of transition metal complexes to the surface. These materials are designed to enhance the fundamental activity of the metal ion, by providing it with an environment tailored to make it as active as possible, and to aid in its recovery afterwards. The heterogenisation of such (normally homogeneous) complexes has attracted a lot of attention, since the heterogeneous equivalents can be much more easily separated and recycled than the... 

Room temperature CO oxidation has been investigated on a series of Au/metal oxide catalysts at conditions typical of spacecraft atmospheres CO = 50 ppm, COj = 7,000 ppm, H2O = 40% (RH) at 25 C, balance = air, and gas hourly space velocities of 7,000- 60,000 hr . The addition of Au increases the room temperature CO oxidation activity of the metal oxides dramatically. All the Au/metal oxides deactivate during the CO oxidation reaction, especially in the presence of CO in the feed. The stability of the Au/metal oxide catalysts decreases in the following order TiOj > FejO, > NiO > CO3O4. The stability appears to decrease with an increase in the basicity of the metal oxides. In situ FTIR of CO adsorption on Au/Ti02 at 25 C indicates the formation of adsorbed CO, carboxylate, and carbonate species on the catalyst surface. 

The structural variations observed for [TpRR ]M(N03) (M = Co, Ni, Cu, Zn Cd) reveal that, for a given [Tp1 ] ligand, the preference for bidentate coordination increases across the series Zn < Co Cu, Ni, and Cd. Significantly, these structural preferences of the nitrate ligand correlate with the activity of the metal-substituted enzymes Zinc, the metal with the greatest tendency to exhibit unidentate coordination of the nitrate ligand, is the most active, while nickel, copper, and... 

The same expression is obtained if electrodes of the second kind are considered as electrodes of the first kind, where the activity of the metal cations depends on the solubility product of the given insoluble salt (cf. Eq. 3.1.26) ... 

Second, as a logical development of the first approach, polyphosphazenes have been synthesized that bear phosphine units connected to aryloxy side groups (37). The phosphine units bind organometallic compounds, such as those of iron, cobalt, osmium, or ruthenium (38). In several cases, the catalytic activity of the metal is retained in the macromolecular system (39). A similar binding of transition metals has been accomplished through nido carboranyl units linked to a polyphosphazene chain (40). 

Dissolution of a zinc-ruthenium alloy in hydrochloric acid leaves an explosive residue of finely divided ruthenium [1], More probably this is the hydride, which may decompose on slight stimulus, the evolved hydrogen probably igniting because of the catalytic activity of the metal. Ruthenium prepared from its compounds by borohydride reduction is especially dangerous in this respect [2],... 

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