INDEX promoter

The various alkali metals may yield slightly different results in terms of catalyst performance. Lithium is slightly preferred over sodium as a melt-index promoter, and both may be preferred over potassium. Such differences have been reported in investigations on silica doped with 5 mol% of alkali metal and calcined at 700 °C. Lithium caused crystallization to form quartz whereas sodium and potassium caused conversion to cristobalite [477,609-612],... 

Various polymers, such as polythiourethanes, polythioethers, and polythioacrylates, are used to produce resins which are transparent, colorless and have a high refractive index and good mechanical properties, useful for the production of optical lenses. Higher refractive indices are promoted by sulfur compounds and especially by esters of mercaptocarboxyhc acids and polyols such as pentaerythritol (41) (see Polymers containing sulfur). 

In the glass (qv) and ceramic industry (see Ceramics), barite can be used both as a flux, to promote melting at a lower temperature or to increase the production rate, and as an additive to increase the refractive index of glass. The viscosity of barite-containing glass often needs to be raised. Alumina in the form of feldspar is sometimes used. To offset any color produced by iron from the barite addition, more decolorizer may be needed. When properly used, barytes help reduce seed, increase toughness and brilliancy, and reduce annealing time. Barite is also a raw material for the manufacture of other barium chemicals. 

The promotional propensity of a promoter, p, can be quantified by defining20 a promotional index, PIp, from ... 

Thus the promotional index PIp is positive for promoters and negative for poisons. In the latter case the definition of PIp coincides with that of the toxicity defined by Lamy-Pitara, Bencharif and Barbier several years ago.21 In the case of pure site-blocking it is PIp=-l. Values of PI02- up to 150 and of PINas+ up to 6000 have been measured as we will see in Chapter 4. 

The table also gives the catalyst material, the operating temperature range, the maximum (for A>1) or minimum (for A<-1) measured A value and the maximum (for p>l) or minimum for (prate enhancement, p, value. It also provides the maximum measured promotion index, PIi5 value. An asterisk in the p column indicates that electrochemical promotion causes also a change in product selectivity. 

Figure 4.26. Transient response of the rate of CO2 formation and of the catalyst potential during NO reduction by CO on Pt/p"-Al2C>396 upon imposition of fixed current (galvanostatic operation) showing the corresponding (Eq. 4.24) Na coverage on the Pt surface and the maximum measured (Eq. 4.34) promotion index PINa value. T=348°C, inlet composition Pno = Pco = 0.75 kPa. Reprinted with permission from Academic Press.

Figure 4.27 presents steady-state potentiostatic r vs 0Na results during NO reduction by H2 on Pt/p"-Al203f2 PInb values well in excess of 4000 are obtained for 0Na values below 0.002. This is due to the tremendous propensity of Na to induce NO dissociation on transition metal surfaces. Since Plj is often found to be strongly dependent on 0, (Figs. 4.26 and 4.27), it is also useful to define a differential promotion index pij from ... 

As previously noted, determination of the promotion index PI0s- of the promoting oxide ions O6 requires knowledge of the coverage of O6 on the... 

The maximum 0os value is thus computed for the transient of Fig. 5.6b to be 0os 0.5. This, in view of the definition of the promotion index, PI, (Chapter 4) and the observed p value (p 16.5) gives a PIQ5- value of the order of 30, in good qualitative agreement with PI0s- values for other Pt catalyzed oxidations.5... 

The electrochemically induced creation of the Pt(lll)-(12xl2)-Na adlayer, manifest by STM at low Na coverages, is strongly corroborated by the corresponding catalyst potential Uwr and work function O response to galvanostatic transients in electrochemical promotion experiments utilizing polycrystalline Pt films exposed to air and deposited on (T -AbCb. 3637 Early exploratory STM studies had shown that the surface of these films is largely composed of low Miller index Pt(lll) planes.5... 

As a consequence of the irregular and rough structure of the xylan particles, entanglements between particles are promoted and this fact may explain the poor flow properties of this polymer (Kumar et al., 2002 Nunthanid et al., 2004). Additionally, rheological parameters of xylan powder have also been studied, such as bulk and tapped densities, Hausner ratio, Carr s index, and angle of repose values, and they are summarized in Table 1. 

The price index is adjusted periodically according to an adjustment factor that is pre-established and exogenous to the company during the lifetime of the regulatory contract, but can be established on the basis of the fulfilment of certain policies by the company in the previous period (for example, R D policies, limits on spending on advertising and promotion and so on). 

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