Catalyst Performance Characteristics

Evaluation of an experimental catalyst for possible commercial use involves a complex range of catalyst performance characteristics. A summary of some of these characteristics is shown below. 

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Activity, selectivity, and yield are key catalyst performance characteristics. The recommended measure of catalyst activity is turnover frequency. Turnover frequency (or rate) is defined as the number of molecules that react per active site per unit time. Activity can also be defined as (1) the reaction rate per unit mass or volume of the catalyst, (2) the space velocity at which a given conversion is achieved at a specified temperature, (3) the temperature required to achieve a given conversion level, or (4) the conversion achieved under specified reaction conditions. Alternative 2 is practical for catalyst ranking. Alternatives 3 and 4 are rather uninformative. For rapid catalyst screening the latter two criteria are acceptable, but no catalyst should be eliminated from further consideration if it is only marginally inferior based on these criteria. 

The processability of resid in FCC and the role of the catalyst have been extensively discussed in the literature[l-4]. Depending on the feedstock, feed pretreatment, unit design, and operating philosophy, the priority of the various catalyst performance characteristics may differ considerably [4,5]. 

TABLE 59 Catalyst Performance Characteristics Obtained in Three Commercial Examples, Showing the Response of Two Catalysts to Cocatalysts... 

Commercial experience has led to optimization of catalyst performance characteristics and octafiner process design such that ultimate xylene yields have increased from the high 60s to greater than 90 wt % on feed. 

Tsipouriari, V., Zhang, Z. and Verykios, X. (1998). Catalytic partial oxidation of methane to synthesis gas over Ni-based catalysts - I. Catalyst performance characteristics, J. Catal., 179, pp. 283-291. 

Polypropylene. PP is a versatile polymer, use of which continues to grow rapidly because of its excellent performance characteristics and improvements in its production economics, eg, through new high efficiency catalysts for gas-phase processes. New PP-blend formulations exhibit improved toughness, particularly at low temperatures. PP has been blended mechanically with various elastomers from a time early in its commercialisation to reduce low temperature brittleness. 

The ROTOBERTY internal recycle laboratory reactor was designed to produce experimental results that can be used for developing reaction kinetics and to test catalysts. These results are valid at the conditions of large-scale plant operations. Since internal flow rates contacting the catalyst are known, heat and mass transfer rates can be calculated between the catalyst and the recycling fluid. With these known, their influence on catalyst performance can be evaluated in the experiments as well as in production units. Operating conditions, some construction features, and performance characteristics are given next. 

Another characteristic of this solution is its proneness to crystallization and polymerization. When parts of the exhaust system are constantly welted by Adblue on the same spot, undesired urea crystals or polymers may form if the exhaust line temperature is lower than 300°C. This phenomenon will result in uncontrolled ammonia production when the crystals or polymers melt or sublimate after being heated at significantly higher temperatures (T > 350°C). This may result in ammonia release. Furthermore, the crystals or polymers can also have an impact on the SCR catalyst cells by reducing the catalyst surface and thus reducing the catalyst performances. 

The results of the catalyst testing are shown in Table 3. The data listed in the table show, that on a per proton basis, catalyst A (based on 7% DVB) has higher activity as compared to resin materials, crosslinked with 12% DVB. This result is in accord with the finding by Petrus et al.,3 that at temperatures higher than 120 °C the hydration is under into particle diffusion limitation and as such, a more flexible polymeric matrix will provide better access to the acidic sites. On a dry weight basis, catalyst D showed the highest activity, which correlates well with the high acid site density found for this resin (Table 2). On a catalyst volume basis, catalyst A has the best performance characteristics followed by catalyst D. 

In summary, the basicity and the strong NiO-MgO interactions in binary NiO/MgO solid solution catalysts, which inhibit carbon deposition and catalyst sintering, result in an excellent catalytic performance for C02 reforming. The characteristics of MgO play an important role in the performance of a highly efficient NiO/MgO solid-solution catalyst. Moreover, the NiO/MgO catalyst performance is sensitive to the NiO content a too-small amount of NiO in the solid solution leads to a low activity, and a too-high amount of NiO to a low stability. CoO/MgO solid solutions have catalytic performances similar to those of NiO/MgO solid solutions, but require higher reaction temperatures. So far, no experimental information is available regarding the use of a FeO/MgO solid solution for CH4 conversion to synthesis gas. 

Ultimately, the catalyst performance of a real fuel cell is of the greatest importance. The DEFC polarization curves for the two PtSn anode catalysts are tested and shown in Fig. 15.9. The characteristic data are summarized in Table 15.4. The PtSn-1 catalyst shows a strongly enhanced electron-oxidation reaction (EOR) activity and much better performance in both the activation-controlled region (low-current density region) and... 

Although several fuel cell technologies are reaching technical maturity, the economics of a fuel cell are not clear. The commercial potential of fuel cells will depend on the ability to reduce catalyst and other expensive materials costs and to manufacture the units at a competitive cost. Many uses of fuel cells place a premium on specific performance characteristics. The relatively simple alkaline fuel cells (AFC)... 

The effects of non-uniform distribution of the catalytic material within the support in the performance of catalyst pellets started receiving attention in the late 60 s (cf 1-4). These, as well as later studies, both theoretical and experimental, demonstrated that non-uniformly distributed catalysts can offer superior conversion, selectivity, durability, and thermal sensitivity characteristics over those wherein the activity is uniform. Work in this area has been reviewed by Gavriilidis et al. (5). Recently, Wu et al. (6) showed that for any catalyst performance index (i.e. conversion, selectivity or yield) and for the most general case of an arbitrary number of reactions, following arbitrary kinetics, occurring in a non-isothermal pellet, with finite external mass and heat transfer resistances, the optimal catalyst distribution remains a Dirac-delta function. 

New catalysts such as a Raney Cu-based system containing Zr49 and ultrafine CuB with Cr, Zr, and Th50 exhibit good characteristics. The improved catalyst performance observed for a Cu-ZnO catalyst with added Pd is explained by the relative ease of hydrogen dissociation by the incorporated Pd particles and then spillover to the Cu-ZnO.51... 

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