Co pressure dependence

The analogous reaction of the 2-chloropyrimidine derivative in 7.62. was also run at elevated temperature under 15 bar CO pressure. Depending on the alcohol, which was either added in excess or used as solvent, the desired esters were isolated in good to excellent yield. If the reaction was run at decreased carbon monoxide pressure, then the dehalogenation of the pyrimidine also became significant.81 The effect of the used ligand was also tested and l,l -bis(diphenylphosphino)ferrocene (dppf) gave the best results. 

Nonphotolytic carbonylations catalyzed by Co2(CO)8 may also occur. With molecular sieves replacing a base, iodoalkanes containing /1-hydrogen atoms carbonylate to esters (equation 206)410. In adition, either Co2(CO)8 or preformed NaCo(CO)4 are capable of car-bonylating or doubly carbonylating benzyl halides under low CO pressures, depending upon the solvent and base employed406,411. 

We can also investigate how the rate of deacfivafing C—C bond formation compares with the rate of initial C—H bond formation. These rates are a function of the strength of inferacfion befween adsorbed carbon atoms and the metal surface (28). When fhe mefhanation reaction expression is generalized such that it can be used to describe the chain-growth reaction, the resultant expression shows the complex CO pressure dependence of the rate of the chain-growth reaction. 

On Mo(100), somewhat similar results were also obtained in CO hydrogenation by Logan et al. (98), where the selectivity for higher hydrocarbons and olefins increased on K addition. In this case, the overall rate of reaction also increased, which may be related to the unusual positive CO pressure dependence for this surface. 

The selectivity data in Table I exhibit virtually the same H2 and CO pressure dependences as the rate data. Such a result is reasonable in terms of the mechanism shown in Figure 4. There (CO)s and Hg compete for the available surface CH3 groups. The relative rates of production of CH4 and C2 chemicals should then be given by ... 

When unsaturated carbides are sought, the purification problem becomes even worse. Since the CO pressure depends on the product of the carbon and oxygen activities, the CO pressure will drop rapidly as the carbide is made more defective. As a result, carbon-deficient carbides or the subcarbides are not only more difficult to purify, but they require a much better vacuum to remain pure if they are heated. 

These are useful expressions k, and kj, are expected to depend on hydrogen pressure but not significantly on CO pressure. The relation between a and Rqq implies a relation between the CO pressure dependence of both kinetics observables. This will be discussed in the next section. Note that, at the same value of a, yield decreases strongly with decrease of kj. 

To deduce the hydrogen and CO pressure dependences from rate expression (16.15) and (16.16), the relation between the apparent rate parameters and elementary rate constants has to be deduced. 

The hydrogen and CO pressure dependence predicted by Eq. (16.19) is very similar to that used in the macrokinetics expressions [15] based on the assumption that CO to activation is rate-controlling. 

Oxidative carbonylation of alcohols with PdCh affords the carbonate 572 and oxalate 573(512-514]. The selectivity of the mono- and dicarbonylation depends on the CO pressure and reaction conditions. In order to make the reaction catalytic, Cu(II) and Fe(III) salts are used. Under these conditions, water is formed and orthoformate is added in order to trap the water. Di-/-butyl peroxide is also used for catalytic oxidative carbonylation to give carbonates and oxalates in the presence of 2,6-dimetliylpyridine(515]. 

Equation (1.5) then allows us to deduce the optimum value of Tads of the Sabatier maximum rate. It can be deduced from Eq. (1.12a). The latter depends on the CO pressure through A. 

An impression of the activity of the different catalysts is given in figure 1. The activity order Cu>Co>Fe corresponds with literature [4]. The N2O pressure dependency for Co-ZSM-5 is given in figure 2. Due to the integral reactor behaviour the relation between conversion and partial pressure shows a curvature, but the reaction order equals 1 for Co, and slightly lower... 

Figure 1 Conversion as a function of Figure 2 Partial pressure dependency of temperature 0.1 kPa N2O and space time Co-ZSM-5 at a space time of 1.52 10 1.44 10 g.s/mol g.s/mol...

The same group has looked into the conversion of NO on palladium particles. The authors in that case started with a simple model involving only one type of reactive site, and used as many experimental parameters as possible [86], That proved sufficient to obtain qualitative agreement with the set of experiments on Pd/MgO discussed above [72], and with the conclusion that the rate-limiting step is NO decomposition at low temperatures and CO adsorption at high temperatures. Both the temperature and pressure dependences of the C02 production rate and the major features of the transient signals were correctly reproduced. In a more detailed simulation that included the contribution of different facets to the kinetics on Pd particles of different sizes, it was shown that the effects of CO and NO desorption are fundamental to the overall behavior... 

One parameter which has so far been neglected in the discussion of the influence of physical conditions on the young Earth is the pressure in rock layers. This has been the subject of investigation by Ohara and co-workers from the Tohoku University in Sendai, Japan, who studied the pressure-dependence of the polymerisation of dry glycine at 423 K and pressures from 5 to 100 MPa. The experiments took between 1 and 32 days. Depending on the pressure, light to dark yellow products were obtained. At low pressures, the colour is probably due to the presence of melanoids. 

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