Catalysts reaction rate

Catalyst Reaction rate to N2 (pmolg s ) Production of NjO Production of NO,... 

GP 4] [R 11] For methanol conversion over sputtered silver catalyst, reaction rates and an activation energy (Figure 3.36) of 14.3 kcal moh were reported (8.5 vol.-% methanol balance oxygen 10 ms slightly > 1 atm) [72]. Since the latter is much lower than literature values (about 22.5-27 kcal moh ), different kinetics may occur or limitations of the reactor model may become evident. 

In the model study by Tolman discussed earlier, the half-life of syn-to-anti isomerization measured by H NMR was found to be 0.36 hours at 30°C. This rate of isomerization is far too slow to affect the stereoselectivity of the hexadiene formed with the catalyst considered here. With the bimetallic catalyst, reaction rates frequently approach 4000 molecules of hexadiene/Ni atom/hour at 25°C (or ca. 1 hexadiene/Ni/second). The rate of insertion reaction d must be at least as fast as this, and the isomerization reaction would have to be even faster to affect the trans/ cis ratio of the product. 

Transition metals can display selectivities for either carbonyls or olefins (Table 20.3). RuCl2(PPh3)3 (24) catalyzes reduction of the C-C double bond function in the presence of a ketone function (Table 20.3, entries 1-3). With this catalyst, reaction rates of the reduction of alkenes are usually higher than for ketones. This is also the case with various iridium catalysts (entries 6-14) and a ruthenium catalyst (entry 15). One of the few transition-metal catalysts that shows good selectivity towards the ketone or aldehyde function is the nickel catalyst (entries 4 and 5). Many other catalysts have never been tested for their selectivity for one particular functional group. 

Figure 12.7 illustrates that, with the applied catalyst, reaction rates of up to tm 4 x 10-7 mol g-icat s could easily be achieved. This corresponds (with an apparent density of the catalyst of 1.2 g cm-3) to a STY of ca. 0.5 mol m 3 s (which is close to the value given in Eq. (28)). 

Catalyst reaction rate l(Pmol relative activity (promVunprom.) ... 

FIGURE 7.2 An isomerization reaction with two parallel paths a direct path D (a —>b), and a mediated path Mt (a + c —> ac), M2 (ac —>b + c). In the first diagram (A), the rate of D and M2 D, thus path M bypasses the direct path D, and c accelerates a through the system, acting as a catalyst (reaction rates indicated by arrow thickness). In the second diagram (B), the rate of Mj D, but in this case D M2, thus c locks up a in complex ac, acting as a competitive inhibitor. 

Catalyst reaction rate lO tnol iWg-1 fresh normalized activity (coked/fresh) coked at 420 C coked at 480°C ... 

Because of the small pores in zeolitic catalysts, reaction rates may be controlled by rates of diffusion of reactants and products. Beecher, Voorhies, and Eberly (4) studied hydrocracking of mixtures of n-decane and Decalin with mordenite catalysts impregnated with palladium. They found that acid leaching of the mordenite produces an aluminum-deficient structure of significantly higher catalytic activity. At least part of this improvement appears to be caused by the decrease in diffusional resistance. They observed that with this type of catalyst, the effective catalyst pore diameter appears to be smaller than calculated owing to the strong interaction or adsorption of hydrocarbon molecules on the pore walls. 

Previous works on the periodic operation of a Trickle Bed Reactor (TBR) have demonstrated that for the hydrogenation of alpha methyl styrene (AMS) to cumene on PCI/AI2O3 catalyst, reaction rates are increased up to 400% with respect to the steady state results (Castellari and Haure (1995)). 

The catalytic combustor was run on diesel fuel during the complete test period. A test campaign comparing exhaust emissions when running on ethanol fuel was performed at Volvo Aero Turbines. These results showed that the catalyst reaction rate and CO/HC/NO emissions were similar. This means that the chosen catalytic combustor can be used as a duel fuel combustor diesel/ethanol. 

All the balances have accumulation, convection, axial dispersion, and reaction terms. The equations include liquid holdup, Bi, and superficial liquid velocity, w. Langmuir-type rate equation, for the main reaction, Equation 15.4, included also an activity correction term a. Kst and in Equations 15.5-15.7 indicate the adsorption parameters for stearic acid and heptadecene, respectively. Equation 15.4 corresponds to a monomolecular transformation of stearic acid via the adsorption of the reactant to the main product. Adsorption terms for stearic acid and heptadecene were used, since both of these compounds contain functional groups enabling adsorption on the active sites of the catalyst Reaction rates were assumed not to be limited by heptadecane adsorp-UoiL Thus, the adsorption term of heptadecane was n ected. In line with the experimental observations indicating catalyst deactivation. Equation 15.4 (Table 15.2) was modified to incorporate the decrease in catalyst activity. In particular, the activity was assumed... 

The internal utilization ratio of ammonia synthesis catalysts depends on particle size and radius of micro-pore of catalyst, reaction rate constant, operation temperature and pressure as well as the difference between the concentration of reaction components in gas bulk and equilibrium concentration etc., among which the most... 

Catalyst Reaction rates/ Surface area/ Specific activity/ (/imol-h m )... 

Maleic anhydride production. The oxidation of benzene to maleic anhydride over a vanadium pentoxide electrode has been studied by Pizzini et ai 90,91 Unfortunately, the quantities of benzene and maleic anhydride were not determined experimentally. Breckner et al. have studied the partial oxidation of butene to produce maleic anhydride over a vanadium phosphate catalyst. Reaction rate and oxygen activity were monitored in order to correlate catalyst selectivity with oxygen activity. The selectivity of the catalyst was found to increase as the oxygen activity of the catalyst decreased. Both the catalyst reactivity and oxygen activity were found to be dependent upon prior treatments. 

Fig. 8. Ln(k) versus temperature of graphite-Fe-K catalyst (x) and iron industrial catalyst ( ). Reaction rate constant "k" in kg MPa°- /(kgj. h).

No antagonism with polymerization catalysts, reaction rates... 

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