Promotion mechanisms

Nevertheless both transient rate analysis24,71 and XPS24 have shown that in both cases the electrochemical promotion mechanism is identical with that obtained with YSZ, i.e. electrochemically controlled migration (back-spillover) ofO2 onto the gas-exposed catalyst-electrode surface.24,71... 

Figure 11.7 confirms that electrochemically induced and controlled O2 backspillover from the support to the metal film surface is the promoting mechanism both in the case of YSZ (Fig. 11.7a) and in Ti02 (Fig. 11.7b). These figures show the Ols spectrum of the Pt film deposited on YSZ and on TiC>2, first under open-circuit conditions (Fig. 11.7aC, 11.7bA) and then under positive current and potential application (Fig. 11.7aB, 11.7bB). Figures 11.7aC and 11.7bC show the difference spectra. In both cases, XPS clearly shows the presence of the O2 double layer, even under open-circuit conditions (Figs. 11.7aA, 11.7bA) and also clearly confirms the electrochemically controlled backspillover of O2 from the YSZ orTi02 support onto the catalyst surface. Note that the binding energy of the backspillover O species is in both cases near 529 eV, which confirms its strongly anionic (probably O2 ) state.31,32...

The good qualitative agreement between eUwR variation and O0 variation shown in Figure 11.11 for the various supports used, underlines again the common promotional mechanism of electrochemically promoted and metal-support interaction promoted metal catalysts. 

They first reported and studied permanent NEMCA and via cyclic voltammetry established the dependence of metal/solid electrolyte capacitance on porous metal film mass, which confirms the O2" backspillover promoting mechanism. 

If the cement is mixed too thinly it may etch the tooth enamel because of its excess acidity (Docking et ai, 1953 Abramovich, Macchi Ribas, 1976). Of course, etching can promote mechanical attachment to the tooth (Ware, 1971). 

Shido, T., and Iwasawa, Y. 1992. Regulation of reaction intermediate by reactant in the water-gas shift reaction on Ce02, in relation to reactant-promoted mechanism. J. Catal. 136 493-503. 

It was found that the rate constant of the forward decomposition of the surface bidentate formate (DCOO ) to produce D2 and C02 increased from 0.34X10 4 sec-1 under vacuum to 5.3 X10-4 sec-1 under ambient water. Electron donors such as NH3, CH3OH, pyridine, and THF also increased the decomposition rate the rate constants of the forward decomposition of the surface formates at 553 K were determined to be 28.0X10 4, 7.7X10 4, 8.1X10-4, and 6.0X10 4 sec-1 under NH3, methanol, pyridine, and THF vapors (0.4 kPa), respectively. It is likely that the driving force for the forward decomposition of the formate is electron donation of the adsorbed molecule to the Zn ion on which the bidentate formate adsorbs. The reactant-promoted mechanism for the catalytic WGS reaction on ZnO is illustrated in Scheme 8.2. 

Anderson that at this level the mechanistic details are a matter of opinion (7). There is, however, a difference as far as the number of surface atoms participating in the reaction is concerned. Mechanism A requires more than one Mechanism C, however, requires only one metal atom. Van Schaik et al. 89) reported skeletal isomerization according to Mechanism A over platinum-rich platinum-gold alloys, whereas over gold-rich catalysts, isolated platinum atoms could promote Mechanism C only. Garin and Gault (82) assumed the formation of a C4 cyclic intermediate with the insertion of a platinum atom as the fourth member of the ring. This concept of Mechanism B would also involve one metal atom. 

To study the promotion mechanism of Pt wire/FSM-16 in the PROX reaction, the Pt nanowires were extracted by HF/EtOH treatment from FSM-16, and the wires were again deposited on the external surface of FSM-16 from the ethanol solution. We found that the resulting external Pt wire/FSM-16 catalyst gave low TOFs (>35) and lower CO selectivity (>30%) in the PROX reaction [32]. This implies that the encapsulation of Pt wires in the silica channels of FSM-16 is a key to promote the selective CO oxidation in the PROX reaction. Furthermore, from the structural characterization by XANES, XPS and IR in CO chemisorption... 

Formation of Metal Oxides Which Promote Mechanical Aspects of... 

Additional work must be completed before these hydration inhibitor treatments will be widely used. However, it appears that combined FPL/inhibitor pretreatments have the potential of producing water stable aluminum oxides with structures that promote mechanical aspects of adhesion in a relatively simple manner. Since mechanical adhesion mechanisms are not greatly affected by water, these pretreatments show promise as a means of increasing the durability of metal/polymer adhesion systems in wet environments. 

Enhanced surface segregation. The variation in catalytic activity with Co/Mo ratio is proposed to be due to a surface enhancement of Co species in a mixed CoMo-sulfide phase, the Co being considered a promoter (127). This model does not specify the promotion mechanism nor does it take account of any role of the support. 

VCPOs catalyze the two-electron oxidation of halides (X- = Cl-, Br-, I ) using activated peroxide through a Lewis acid-promoted mechanism (in contrast to possible redox cycling at the V center). Peroxide is bound to V in r/ -fashion after release of the apical oxygen (Littlechild, 2002) this release is catalyzed through the... 

Hirasawa, T., et al. 1985. Promoting mechanism by bile salt related to water absorption in drug rectal absorption. J Pharmacohiodyn 8 211. 

To summarize, there is now strong evidence that sleep disturbances encountered in major depression are associated with an increase of wake-promoting mechanisms linked to a stress-related hyperarousal reaction implicating the CRH and the LC-AN systems. 

The mechanism for basic hydrolysis begins with attack by hydroxide on the electrophilic carbon of the cyano group. Protonation gives the unstable enol tautomer of an amide. Removal of a proton from oxygen and reprotonation on nitrogen gives the amide. Further hydrolysis of the amide to the carboxylate salt involves the same base-promoted mechanism as that already discussed. 

The Sml2-promoted mechanism follows a pathway originally proposed for the Na-Hg reductions (Scheme 4.31). The exact role of DMPU is not clear, but rate enhancement may be due to lowering of the oxidation potential of Sml2. 

CO dissociation but also for CO insertion. A similar promotion mechanism was previously proposed for RhFe and PdFe carbonyl cluster-derived catalysts which exhibited substantial improvement in C1-C2 alcohol production in CO hydrogenation. The conventional IrFe catalysts prepared from coimpregnation of IrCl4 and FeCls provided poor yield and selectivity toward alcohols versus the corresponding cluster-derived catalysts. The bimetallic IrFe cluster precursors offer the advantages of higher metal dispersion and more uniform distribution of active IrFe sites over the conventional salt-derived catalyst preparation. 

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