Dependence on catalyst composition

Figure 16.8 Comparison of feed and product catalysts, (b) the formation of different composition from light cycle oil hydrocracking distributions of substituted single-rings showing (a) essentially complete conversion depending on catalyst composition. Catalysts of feed two-ring compounds on four different 1—4 differ in metal and acid function.

Figure 4. Phenol conversion, and o-cresol and 2,6-xylenol selectivity dependence on catalyst composition and reaction temperature with a feed composition of MeOH PhOH = 5 1, at time on stream = 3h. Note that 2,6-xylenol selectivity increases with phenol conversion, and at the expense of o-cresol with all catalyst compositions, indicating the first order conversion dependence and the sequential methylation, respectively.

Figure 12. Activation energy dependence on catalyst composition for Cul-xCoxFe204 catalysts. Note the relatively high Ea with end compositions than the intermediate compositions of catalyst.

As COR and OER occur simultaneously in the cathode, their kinetics are particularly important in evaluating carbon-support corrosion. The kinetics of OER is material-specific, dependent on catalyst composition and electrode fabrication.35,37 -39 A number of OER kinetics studies were done on Pt metal electrodes.37-39 However, there is a lack of OER kinetics data on electrodes made of Pt nano-particles dispersed on carbon supports. Figure 2 shows the measured OER current density with respect to the overpotential defined by Eq. (6).35 The 02 concentration was measured at the exit of a 50-cm2 cell using a gas chromatograph (GC). The 02 evolution rate (= 02 concentration x cathode flow rate) was then converted to the OER current density, assuming 4e /02 molecule. Diluted H2 (10%) and a thicker membrane (50 p,m) were used in the measurement to minimize H2 crossover from anode to cathode, because H2 would react with 02 evolved at the cathode and incur inaccuracy in the measured OER current density. Figure 2 indicates that the OER... 

The following table (Table VI.), shows an example of vanadium mobility and its dependence on catalyst composition. 

Aromatic imides are another type of product which can be synthesized by catalytic ammoxidation. o-Xylene is converted over vanadium-titanium oxide catalysts to tolunitrile and then, depending on catalyst composition and reaction conditions, phthalimide or phthalonitrile can be selectively synthesized (Scheme 20.3) [94]. 

Davis26 pointed out in his review on FT synthesis mechanism that the reaction pathway is also dependent on catalyst compositions and operation conditions. Their experimental data on FT synthesis with iron catalysts at low temperatures suggested that instead of carbide mechanism, an oxygenate intermediate, similar as the formate species responsible of the WGS reaction, existed on the surface and initiated carbon chain propagation. The final chain termination step was accompanied by elimination of the oxygen atom. 

Table 1 presents the dependence of n-hexane conversion on reaction temperature and platinum content in the catalyst. Hexane conversion increased when the reaction temperature was increased from 550°C to 650°C. Hexane conversion was also found to depend on catalyst composition at 550°C. Increasing Pt content in the catalyst from 0.15 to 0.35% lead to an increase in n-hexane conversion from 10 to 35%. Nearly complete conversion of n-hexane was observed on the catalysts with higher Pt content. 

Influence of Catalyst Composition. Coke deposition on the catalyst depends on catalyst composition. The individual characteristics of both catalytic functions, metal and acid, are important as well as how they are balanced during the reaction. 

The kinetics of the whole process are quite particular in this sense that the rate equation is the product of two terms, one N, the number of sites, depending on catalyst composition Rm and gas composition, and a classical one (e.g. a Langmuir-Hinshelwcxxl... 

One of the great benefits of the SOFC is that it can utilise a wide range of fuels, as described in Chapter 12. The fastest reaction at the nickel anode is that of hydrogen. But other fuels can also react directly on the anode, depending on catalyst composition. For example, carbon monoxide can react on Ni/YSZ, but has a higher overpotential than hydrogen [3 5]. Also, methane can react on the... 

All these observations show that the catalytic activity of tetrabutoxytitanium depends on the composition of the medium used. When alcohol is used in excess, the catalyst is in a favourable neighbourhood since titanium can be complexed by two alcohol molecules. 

There is a wide variety of solid electrolytes and, depending on their composition, these anionic, cationic or mixed conducting materials exhibit substantial ionic conductivity at temperatures between 25 and 1000°C. Within this very broad temperature range, which covers practically all heterogeneous catalytic reactions, solid electrolytes can be used to induce the NEMCA effect and thus activate heterogeneous catalytic reactions. As will become apparent throughout this book they behave, under the influence of the applied potential, as active catalyst supports by becoming reversible in situ promoter donors or poison acceptors for the catalytically active metal surface. 

Evaluating the results a clear kinetic picture of the catalysts has been obtained. In the steady state the active sites in Fe- and Cu-ZSM-5 are nearly fully oxidized, while for Co only -50% of the sites are oxidized. The former catalysts oporate in an oxidation reduction cycle, Fe /Fe and CuVCu. Coi in zeolites is hardly oxidized or reduced, but ESR studies on diluted solid solutions of Co in MgO indicate that Co -0 formation is possible, rapidly followed by a migration of the deposited oxygen to lattice oxygen and reduction back to Co [36]. For Fe-ZSM-5 such a migration has been observed, so a similar model can be proposed for the zeolitic systems. Furthermore, it is obvious that application of these catalysts strongly depends on the composition of the gas that has to be treated. 

Amberntsson, A., Persson, H., Engstrom, P. et al. (2001) NOx release from anoble metal/BaO catalyst dependence on gas composition. Appl. Catal. B, 31, 27. 

The state of a given small particle in a catalyst depends on the composition of the surrounding gas atmosphere, the temperature and the pressure. A rather extreme illustration is provided by the disintegration of rhodium particles in CO. 

All Keggin-type POMs exhibit an initial unsteady catalytic behavior, which can last from a few hours up to 100 hours, depending on the composition of the POM and on the method employed for its preparation. The progressive variation of catalytic performance occurring during this equilibration period is shown in Figure 14.5, where the conversion of isobutane and the selectiviy to the products are plotted as functions of the reaction time. The catalyst was a... 

Here we discuss dispersion polymerizations that are not related to vinyl monomers and radical polymerization. The first one is the ring-opening polymerization of e-caprolactone in dioxane-heptane (30). A graft copolymer, poly(dodecyl acrylate)-g-poly(e-caprolactone), is used as a stabilizer. The polymerization proceeds via anionic or pseudoanionic mechanism initiated by diethylaluminum ethoxide or other catalysts. The size of poly(caprolactone) particles depends on the composition of stabilizer, ranging from 0.5 to 5 i,m. Lactide was also polymerized in a similar way. Poly(caprolactone) and poly(lactide) particles with a narrow size distribution are expected to be applied as degradable carriers of drugs and bioactive compounds. 

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