Selectivity overall

The arrangement which gives the highest overall selectivity can only be deduced by detailed sizing and costing calculations specific to the reaction system. 

The following details mathematical expressions for instantaneous (point or local) or overall (integral) selectivity in series and parallel reactions at constant density and isotliermal conditions. An instantaneous selectivity is defined as the ratio of the rate of formation of one product relative to the rate of formation of another product at any point in the system. The overall selectivity is the ratio of the amount of one product formed to the amount of some other product formed in the same period of time. 

The conjugate addition of trichloromethylmagnesium chloride, prepared from 2.7 equivalents of isopropylmagnesium chloride and one equivalent of carbon tetrachloride at 110 C, to 8 (R1 = CH3) gave 9 with overall selectivity of 98 2 in 99% yield31. 

Besides its widespread use for investigating the mechanism of redox processes, spectroelectrochemistry can be usefiil for analytical purposes. In particular, the simultaneous profiling of optical and electrochemical properties can enhance the overall selectivity of different sensing (30) and detection (31) applications. Such coupling of two modes of selectivity is facilitated by the judicious choice of the operating potential and wavelength. 

These results show that important performance benefits are obtained by the addition of Au and KOAc to a palladium catalyst. Gold (Au), when added to palladium (Pd), enhanced the VAM production rate of the catalyst (VAM STY) substantially while it decreased the overall selectivity of the catalyst. This is true in both cases Pd-Au w/KOAc vs. Pd w/KOAc (764 vs. 100 93.6% vs. 95.4%) and Pd-Au vs. Pd (594 vs. 124 91.6% vs. 94.7%). Conversely, KOAc increased the selectivity of the catalyst whether or not Au is used. In the most appetizing example (Pd-Au w/KOAc vs. Pd-Au), KOAc improved the selectivity of the catalyst by 2.0% while it additionally improved the production rate of die ca yst 30%. KOAc only increased the production rate of the catalyst in the presence of Au. KOAc decreased the VAM production rate of the catalyst on its addition to the Pd catalyst where Au was absent. 

In the presence of Au/C catalyst, the reaction pathway was studied concluding that glycerate/tartronate amounts represents the probe of path a and glycolate of path b [41c] (Scheme 1). The overall selectivity of the reaction is dictated by the balance of path a and b and represents the most valuable parameter to be considered for evaluating the effectiveness of a catalyst. 

The elementary reaction energies and thermodynamics for methanol dehydrogenation have been shown to be significantly influenced by electrode potential. The oxidation pathways become much more favorable at higher potentials. The relative barriers of O—H to C—H bond activation decrease with increasing potential, which decreases the overall selectivity to CO and CO2 and increases the yield of formaldehyde. This is consistent with experimental studies. The oxidation of CO intermediates appears to occur via adsorbed hydroxyl intermediates. The hydroxyl intermediates are more weakly held to the surface than atomic oxygen, and thus have significantly lower barriers for the oxidation of CO. 

Figure 40.5 compares the conversion of ammonia and -hexane for catalysts with composition SnA /Nb/Sb x/0.2/1/3, while Figure 40.6 reports the overall selectivity to iV-containing compounds. Surprisingly, the samples containing the greater amount of Sn were the most active. This result was quite unexpected, because... 

Currently the reaction is carried out using cobalt based catalysts with severe penalties in terms of harsh operating conditions (80 bar CO/H2, 200°C). In addition, substantial loss of substrate (ca. 10%) to hydrogenation makes the overall selectivity to the linear alcohol ca. 80% [15]. Rhodium based systems are capable of giving higher selectivities (>90%) to the desired linear aldeyde product under milder conditions (20 bar, 100°C) [13]... 

It is apparent from this short introduction that optimal control of the overall selectivity of olefin oligomerization reactions depends on the simultaneous control of several different types of selectivity. 

Overall selectivity in HIC is a composite effect created by several different mechanisms, each of which affect protein retention in a different way. Different... 

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