Continuous-Layer Catalysts

A new catalyst systan developed by 3M called Nanostructured Thin Film (NSTF) is the first practical example that managed to find a delicate balance by utilizing the 

ELECTROCATALYST DESIGN IN PROTON EXCHANGE MEMBRANE FUEL CELLS 

FIGURE 13.6 (a) Dispersed catalyst ( 3 nm Pt on 200 nm carbon black aggregates of 40nm 

NSTF electrodes also may offer some benefits from a manufacturing standpoint thanks to their fabrication method which can be solely via dry roll-to-roll processes 

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Time courses of rate of hydrogen generated from decalin with carbon-supported platinum catalyst at various feed rates in bench-scale continuous operation. Catalyst platinum nanoparticles supported on ACC (5 wt-metal%), 0.29 g (one layer, ), 0.58 g (two layers, A), and 0.87 g (three layers, O). Feed rate of decalin 1.5, 2.0, 2.5, 3.0, and 5.0 mL/min. Reaction conditions boiling and refluxing by heating at 280°C and cooling at 25°C. 

It was supposed that the actual rate of reaction at the surface of the catalyst was great compared with the rate at which the reacting substances could diffuse through a continuous layer of the retarding gas. 

Another solution to both the carbon support and the ionomer contact issue is to use a Pt catalyst that has no support and is embedded in the membrane such as the Nano-structured thin film (NSTF) catalyst being developed by 3M [5, 81]. A SEM of the NSTF-Pt catalyst is shown in Fig. 17.13. hi addition to not having a carbon support to corrode, this catalyst system is much less susceptible to Pt dissolution because the small whiskers are coated with a continuous layer of Pt, not Pt nanoparticles, and so behaves more like bulk Pt. MEAs made with these electrodes... 

There are, however, continuing difficulties for catalytic appHcations of ion implantation. One is possible corrosion of the substrate of the implanted or sputtered active layer this is the main factor in the long-term stabiHty of the catalyst. Ion implanted metals may be buried below the surface layer of the substrate and hence show no activity. Preparation of catalysts with high surface areas present problems for ion beam techniques. Although it is apparent that ion implantation is not suitable for the production of catalysts in a porous form, the results indicate its strong potential for the production and study of catalytic surfaces that caimot be fabricated by more conventional methods. 

For these gradients, continuity requires that everything that reacted inside, had to diffiise through the outside layer of the catalyst. 

Concentration gradient inside the catalyst particle. The continuity statement, at the catalyst surface, is similar to Pick s first law for diffiasion. The reaction rate is equal to the diffusion rate at the outside layer of the catalyst... 

Temperature gradient in the catalyst particle. Continuity in the outermost layer of the catalyst requires that all the heat generated inside has to cross this layer. The continuity statement in the outermost layer is now similar to Fourier s lav/ for thermal conduction. 

Figure 4-8 shows a continuous reactor used for bubbling gaseous reactants through a liquid catalyst. This reactor allows for close temperature control. The fixed-bed (packed-bed) reactor is a tubular reactor that is packed with solid catalyst particles. The catalyst of the reactor may be placed in one or more fixed beds (i.e., layers across the reactor) or may be distributed in a series of parallel long tubes. The latter type of fixed-bed reactor is widely used in industry (e.g., ammonia synthesis) and offers several advantages over other forms of fixed beds. 

After the calculated amount of hydrogen had been absorbed, the catalyst was filtered off, the solution was concentrated in vacuo, and the residual syrup was dissolved in ice water. Benzene was added and the mixture was made alkaline with an excess of concentrated ice cold potassium carbonate solution. The temperature was kept low by continuous addition of ice, and the benzene layer was separated and dried with sodium sulfate. The dried benzene solution was concentrated in vacuo and the residual oil was distil led in vacuo. BP 30 mm = 175°-1 B2°C,... 

Because hydrolytic reactions are reversible, they are seldom carried out in batch wise processes [26,28,36,70]. The reactor is usually a double jacket cylindrical flask fitted with a reflux condenser, magnetic stirrer, and thermometer connected with an ultrathermostat. The catalyst is added to the reaction mixture when the desired temperature has been reached [71,72]. A nitrogen atmosphere is used when the reactants are sensitive to atmospheric oxygen [36]. Dynamic methods require more complicated, but they have been widely used in preparative work as well as in kinetic studies of hydrolysis [72-74]. The reaction usually consists of a column packed with a layer of the resin and carrying a continuous flow of the reaction mixture. The equilibrium can... 

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