Single catalysts performance

But when the contents of Nafion ionomer was increased from 30 to 45 % to find out the better electrode structures, the Pt-Ru/SRaw, which had showed the lowest single cell performance, became the best electro-catalyst. By this result one can conclude that as long as the structure of the electrode can be optimized for the each of new electro-catalysts, the active metal size is a more important design parameter rather than inter-metal distances. Furthermore, when the electro-catalysts are designed, the principal parameters should be determined in the consideration of the electrode structures which affect on the electron conduction, gas permeability, proton conductivity, and so on. 

It would certainly be desirable to evaluate catalyst performance and understand size and stmctural effects directly under the conditions of fuel cell operation. However, determination of kinetic parameters in a single-cell fuel cell is associated with a number of limitations. Let us consider some of them. 

The catalytic performances obtained during transalkylation of toluene and 1,2,4-trimethylbenzene at 50 50 wt/wt composition over a single catalyst Pt/Z12 and a dualbed catalyst Pt/Z 121 HB are shown in Table 1. As expected, the presence of Pt tends to catalyze hydrogenation of coke precursors and aromatic species to yield undesirable naphthenes (N6 and N7) side products, such as cyclohexane (CH), methylcyclopentane (MCP), methylcyclohexane (MCH), and dimethylcyclopentane (DMCP), which deteriorates the benzene product purity. The product purity of benzene separated in typical benzene distillation towers, commonly termed as simulated benzene purity , can be estimated from the compositions of reactor effluent, such that [3] ... 

Model studies on single crystal surfaces are also helpful in developing an understanding of the effects of surface additives on catalyst performance. Electronegative, electroneutral (i.e. metals) and electropositive additives can all be studied. The influence of additives on the bond strengths and structure of... 

Figure 16.n Hydrocracking catalyst performance in single stage recycle as a function of zeolite content and unit cell size. 

Figure 3.3 Single cell performances of catalysts supported on various CNFs (a) T-CNF, (b) P-CNF, (c) thick H-CNF, (d) very thin H-CNF and (e) E-TEK catalyst. CNE-supported catalysts, Pt-Ru 40wt% (Pt 1.33, Ru 0.67 and CNE 3 mgcm ) E-TEK catalyst, Pt-Ru 60wt% (Pt 2, Ru 1 and CNE 2mgcm ).

Figure 3.6 (a) l-V curves and (b) single cell performances of Pt-Ru 40wt% catalysts supported on as prepared H-CNF, nanotunneled H-CNF and 60wt% E-TEK catalyst examined at 30, 60 and 90°C. 

The single cell performance of the catalyst supported on nanotunneied mesoporous H-CNE was found to be affected by the pH used in the impregnation procedure, which was controlled by adding 1 M NaOH solution. The highest maximum power density of 169 mWcm was produced with the catalyst obtained at pH 3-4. Accurate control of the pH in the impregnation procedure is therefore an important factor for improving the catalytic activity. 

The single cell performance and the maximum power density of the Pt-Ru 40 wt% catalyst supported on thin H-CNF are shown in Figure 3.8. The maximum power densities were 76, 140 and 246mWcm at 30, 60 and 90°C, respectively. The present nanodispersion treatment is therefore very effective in dispersing thin CNFs. 

Figure 3.8 Single cell performance of the catalyst supported on highly dispersed thin H-CNF examined at 30 60 and 90 C.

Organometallic catalysts and reagents normally mediate a single transformation however, their expense reqnires high turn over efficiency. Another way to increase then-efficiency is to participate in seqnential reactions where multiple transformations are performed seqnentially in the same pot by a single catalyst or with complementary catalysts. 

Three different Cr-Co spinels were prepared and tested as catalysts for the oxidation of methane in the presence of SO2, a typical catalyst poison. The spinels were prepared from nitrate precursors using a co-precipitation method, followed by calcining at three different temperatures, (400, 600 and 800 °C) for 5 hours. Characterisation results indicate that the catalyst calcined at 800 C presents a structure of pure spinel, whereas the presence of single oxides is observed in the catalyst calcined at 600 C, and the catalysts calcined at 400 C presents a very complex structure (probably a mixture of several single and binary oxides). Experiments show an important influence of calcining temperature on the catalyst performance. In absence of SO2, catalysts calcined at 400"C and 600 C performs similarly, whereas the activity of the catalysts calcined at 800 C is worse. When sulphur compounds were added to the feed, catalyst calcined at 600"C deactivated faster than the other two catalysts. 

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