Catalyst promoter INDEX

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.

The promotional index, Pip [Eq. (2)]. After the establishment, via the use of surface spectroscopy (XPS [87,88], UPS [89], TPD [90], PEEM [91], STM [92], work function measurements [93]) but also electrochemistry (cyclic voltammetry [90], potential programmed reduction [94], AC impedance spectroscopy [43,95]), that electrochemical promotion is due to the potential-controlled migration (reverse spillover or backspillover) [13] of promoting ionic species (0 , Na", H, F ) from the solid electrolyte to the gas-exposed catalyst surface, it became clear that electrochemical promotion is functionally very similar to classical promotion and that the promotional index PI, already defined in Eq. (2), can be used interchangeably, both in classical and in electrochemical promotion. 

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... 

Davison CP-3 Combustion Promoter, by itself, has a very low SOx Index. At a 0.37% level in a catalyst blend, it contributes less than 0.3 of an SOx Index unit at regenerator temperatures of 1250 F to 1350 F. Its contribution to SOx reduction derives from its ability to catalyze the oxidation of S0 to SO (Equation 2 in Figure 1). ... 

Data on four SOx catalyst systems show that the presence of combustion promoter causes an increase in the SOx Index at a regenerator temperature of 1250 F (Table II). This implies that, without combustion promoter, the rate-controlling step in SOx reduction is the oxidation of SO to SO (Equation 2 in Figure 1). The use of combustion promoter increases the rate of oxidation of SO to SO, thereby causing an increase in the SOx Index. 

Fig. 14. The melt index of the polymer, which reflects the catalyst termination rate, is also promoted by titania, at least at the lower activation temperatures.

When it is considered that the base-catalysed reaction starts with the formation of carboanion on the methylenic group by the abstraction of proton, the acid dissociation constant (pKa) would be one of the indexes for the difficulty of the reaction. Although there are no good relationship between the product yield and the pKa value, it is clear that this catalyst could not promote the reaction with reactant 2 of high pKa value. The tendency of catalytic property for these four condensations (entry 1-4) is similar to that over 3-aminopropyl-functionalised silica gel catalyst prepared through silylation [18]. 

FIGURE 107 Fluidity (inverse of melt viscosity) of polymers made with cogelled Cr/silica-titania catalysts of varying titania contents. In this plot, the fluidity (similar to melt index) is increased (lower MW) by titania, but titania also promotes sintering at high temperatures. (Ti02 listed in mol%.)... 

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],... 

Aromatic fractions can be alkylated with olefins to produce products which are used as synthetic lubricants.An aromatic fraction boiling between 160 and 210°C is generally alkylated with Cm to Cw olefins in a ratio of about 2 1. A higher-boiling aromatic fraction (boiling between 210 and 260°C) is reacted with Cs to Cw olefins in a ratio of 1 3. Aluminum chloride promoted with hydrogen chloride is the catalyst normally used. When the alkylated aromatics are blended with thickeners such as polyisobutylene, the mixture obtained is an excellent lubricant with a good viscosity index, stability, and pour point. 

The high isocyanate index of catalyst system will promote the formation of isocyanate structures. 

In catalyst exploratory studies, one normally screens a wide variety of experimental catalysts with a standard feed. A catalyst that does not activate the most refractory portion of the feed might well be evaluated by a high-order kinetics. But if the performance of the catalyst is improved (for instance, by the incorporation of a more effective promoter) so that there is no longer a reffactory component, then a low overall order would have to be used in evaluating the improved catalyst. In process research work, one generally runs different feeds on a selected catalyst over a wide range of conditions. The overall reaction order is e3q)ected to increase when switching from an easy feed to a hard feed. The extent of this increase could be viewed as an index of feed refractoriness. The overall order is expected to... 

Finally, catalysis is not confined to well-defined. Miller-indexed metal surfaces. One area of recent interest is in the use of certain minerals to catalyze reactions. Some aluminosilicates—minerals with mixed alumina and silica structures—have pores in which molecules can enter and react catalytically [Figure 22.25(a)]. One type of aluminosilicate is called zeolite, shown in Figure 22.25(b). Thanks to the pores in zeolites (which can vary in size and geometry depending on the exact type of zeolite), the properly sized reactant molecules can enter the structure and a particular reaction can be promoted. In fact, it is thought that such minerals are the future of designed catalysts that can be used to promote a preferred chemical reaction—if the pore size is just right. 

A tris(4-bromophenyl)ammonium hexachloroantimonate catalyst has been utilized to promote a cation radical mechanism in the Diels-Alder cycloaddition polymerization of a bis(diene) with an ionizable bis(dienophile) (Scheme 2). The polymers were obtained with molecular weights up to ca 10 000 and a polydispersity index of ca 2. The electron-transfer reactions of phenols and its derivatives are also important to the polymer industry for the stabilization of polymers, fats and oils. Pulse radiolysis of naphthols and hydroxybiphenyls in n-butyl chloride at room temperature forms two species-phenol-type radical cations and phenoxyl-type radicals. Two different electron-transfer channels are proposed. The naphthol and hydroxybiphenyl radical cations show increased stability compared with phenol radical cations, presumably due to extensive delocalization over the whole aromatic system. 

In some applications, narrow molecular weight distributions are desirable. Polydispersity indexes in the range of 3-4 have been reported for systems in which the catalyst is supported on MgCl2 (selective promotion of certain types of sites ) or when additives are used (selective poisoning of certain types of sites ). Single-site (EXXPOL) catalysts have recently been announced, They are reportedly capable of producing polyolefins with a minimum polydispersity index of 2. As this is written, the tot is being commercialized. ... 

The magnesium supports used for polyethylene catalysts could be modified for use in polypropylene production, and magnesium chloride proved to be the most suitable when used with a Lewis base election donor. Milled magnesium chloride was known to have the same layer stracmre as a- and y-titanium trichloride with the quadrivalent titanium ion (0.068 nm diameter), being about the same size as the divalent magnesium ion (0.066 nm diameter). In 1968, Montedison and Mitsui Petrochemical Industries both disclosed the production of a highly active, very steieospecific catalyst that contained about 3% titanium on a magnesium chloride support, promoted with a Lewis base, such as ethyl benzoate. The polymer produced contained less than 1 ppm titanium with an isotactic index of more than 90%, which was improvement on the product made with previous catalysts. 

---