Catalyst performance, comparison

Neathery JK. Davis BH. FT catalyst performance comparison between pilot-scale SBCR and CSTR systems. Catal. Today 2003 84 3-8. 

Characterization of catalytic phenomena at oxide surfaces includes (1) characterization of established catalyst surfaces to improve the catalytic performance, (2) characterization of new catalysts in comparison with conventional catalysts, (3) characterization of specific model surfaces such as single crystals and epitaxial flat surfaces to transfer the knowledge so obtained to catalytic systems or even to create a new type of catalyst, and (4) characterization of catalysis... 

The effect of further increase of the high H2 to CCI2F2 ratio on the catalyst performance is depicted in Figure 4. In this experiment the ratio was doubled to 20 after 680 hours. The steady-state catalyst performance is not only more enhanced at the ratio of 10, but it is also reached far more quickly in comparison to the results in Figure 3b. However, an increase of the ratio to 20 does not lead to a further increase in catalyst performance and at this ratio the catalyst also tends to deactivate. 

Table 41.3 shows a performance comparison of Pt/Pd TUD-1 with a commercial Pt/Pd catalyst (26). The feedstock is a typical straight run gasoil ( SRGO ), a distillate precursor to diesel fuel. Under identical test conditions, the TUD-1 catalyst achieved 75% aromatics saturation versus 50% for the same volume of commercial catalyst. This superior result is particularly interesting because the TUD-1 catalyst had a much lower density than the commercial material, so that less catalyst by weight was required in the reactor. 

Saturated complex polyesters, particularly, poly (butylene terephthalate) (PBT) are used as engineering thermoplastics possesing good thermo - and wearstability, excellent moulding. These properties also allow to use them as matrix material for polymer composites [1], One of the perspective ways of search of effective catalysts for such systems is kinetic study of the reesterification model reaction, performed in the presence of various catalysts and comparison it with the results of the similar reaction without catalyst. Clarification on the example of model system of the most effective catalysts list allows to use them for obtaining both filled and nonfilled PBT and compare catalytic activity of various catalysts. The purpose of the... 

Hence the dimension ("the order") of the reaction is different, even in the simplest case, and hence a comparison of the two rate constants has little meaning. Comparisons of rates are meaningful only if the catalysts follow the same mechanism and if the product formation can be expressed by the same rate equation. In this instance we can talk about rate enhancements of catalysts relative to another. If an uncatalysed reaction and a catalysed one occur simultaneously in a system we may determine what part of the product is made via the catalytic route and what part isn t. In enzyme catalysis and enzyme mimics one often compares the k, of the uncatalysed reaction with k2 of the catalysed reaction if the mechanisms of the two reactions are the same this may be a useful comparison. A practical yardstick of catalyst performance in industry is the space-time-yield mentioned above, that is to say the yield of kg of product per reactor volume per unit of time (e.g. kg product/m3.h), assuming that other factors such as catalyst costs, including recycling, and work-up costs remain the same. 

FIGURE 15.9. Performance comparison of RSn anode based direct ethanol fuel cells at 90°C. Anode catalysts Carbon supported PtSn with a R loading of 1.5 mg/cm, ethanol concentration 1.0 mol/L, flow rate 1.0 mL/min. Cathode (20 Pt wt.%, Johnson Matthey Inc.) with a R loading of 1.0 mg/cm, Pq2 = 2 bar. Electrolyte Naflon -115 membrane. 

The reactions with nG-105 dendrimers show a different trend. Enhanced catalytic performance was observed with increasing dendrimer generation (77.3% yield, 97.2% selectivity, 15.5% ee for Gl 85% yield, 98% selectivity, 37% ee for G4). This comparison indicates that the introduction of an alkyl spacer not only facilitates the access of reactant to the catalytic active sites but also prevents the formation of frozen-in conformations and thus different chiral active sites. However, when the fifth-generation dendrimer is reached, the multiple interactions between end groups become more pronounced, which leads to a decrease in the catalyst performance (68% yield, 95.3% selectivity, 17.6% ee). 

Similar trends were found for the palladium leaching values when leaching fresh catalysts. However, the overall amount of palladium leached is higher in this case. The results of the leaching tests performed one day after the catalyst preparation show values between 140 and 240 ppm for the reduced and of 30 to 60 ppm for the non-reduced catalysts. A comparison of the decrease of metal leaching over time shows different aging effects for the dry catalysts compared to the wet catalysts of... 

The turnover frequency allows performance comparison between different catalyst systems, biological and/or non-biological. Its threshold is at 1 event per second per active site. According to the definition, a turnover frequency can be determined only if the number of active sites is known (Chapter 9, Section 9.2.3). For an enzyme reaction obeying Michaelis-Menten kinetics, Eq. (2.15) holds. 

Since the liquid hourly space velocity is a ratio that involves the use of the volume of catalyst in the reactor, it is also possible to use the data to estimate the additional catalyst required to increase the efficiency of the process. This is especially relevant when the activity of different catalysts is to be compared, and such comparisons are only meaningful if estimations can be made of the quantities of catalyst required to obtain a predetermined performance. For example, to intimate that one catalyst is twice as active as another catalyst signifies that one unit of the first catalyst will function as efficiently as two units of the second catalyst. Such differences in catalyst performance can, however, only be deter-... 

Fig. 10.16 Comparison of Pt-ceria-based catalysts performances (a, b) CO conversion, (c) OSC, as a function of temperature (°C) under various operating conditions.

Only very low catalyst concentrations down to 5 x 10-5 kmol/m3 are consumed that keeps also the catalyst inventory very small [266], Only 0.08 mg of Rh and about 0.2 mg-13 pg of the very expensive chiral ligands (about 300-1000 /g), depending on their molecular weight, are consumed. Finally, a performance comparison for three different reactors was made for the substrate methylacetamidocinnamate and the two rhodium diphosphine complexes Rh/Josiphos and Rh/Diop (see Figure 4.57). The first reactor was a commercial Caroussel reactor (Radleys... 

Figure 4.57 Reaction performance comparison of three reactors with the most active catalysts Rh/Josiphos and Rh/Diop. Caroussel (car), helical falling-film microreactor (p) and Parr (batch) reactor (by courtesy of Elsevier) [266]. 9% conv. and 46% conv. denote a fixed conversion of 9 and 46%, respectively, which have to be achieved.

Figure 5. Comparison of catalyst performance between microbalance (filled symbols) and fixed reactor (open symbols).

Catalyst Screening Results. A comparison of the catalysts performance is given in Table VIII. Shell 214, (nickel-molybdenum (Ni-Mo)) on alumina, is the best among the five types of catalysts tested with Shell 244, Co-Mo on alumina being nearly as good. It achieved high removal of heteroatoms with the least hydrogen consumption. The... 

Table I compares results achieved when seven variables that may affect the performance of a particular catalyst were tested one-at-a-time with results from a statistical design (fractional factorial) approach. In this comparison, a shift in measured performance is assumed to be real if it represents at least twice the uncertainty of the measuring technique. The one-at-a-time strategy, still prevalent among many catalyst researchers, requires 48 experiments to determine with 95% confidence which variables significantly impact catalyst performance. Whereas, with the fractional factorial approach, this same information was obtained in only 16 experiments with a 98.5% confidence level. The fractional factorial approach also shows possible interactions among the variables the classical one-at-a-time approach does not.

Catalyst Composition - Effect on Performance. Comparison of catalyst selectivities are best made at equal conversions. It was previously shown that selectivity of CO hydrogenation to oxygenates decreases with increasing conversion. For example, selectivity decreased linearly from 35% at 4% conversion to 20% at 18% conversion for Rh/Al203 catalysts at 250 C.(10)... 

The study was carried out in relatively small isothermal reactors without recycle, constructed fortesting and comparison of different catalysts and feedstocks. Detailed information about catalyst performance under different conditions can be efficiently obtained under very controlled conditions in such equipment (/). However, exact predictions of the performance of a commercial reformer unit consisting of 3-4 adiabatic reactors will need detailed kinetic and reactor modeling, which is not included in this paper. 

Performance comparison after deactivation with Ni and V of an FCC catalyst and... 

---