Reforming catalyst layer

Obviously, it is unfeasible to process polymers directly in the vapour phase. Most gas phase operations feature a fluidized bed, either constituted of inert sand particles, or of a cracking or reforming catalyst. The plastics fed into the bed are almost immediately melted, coating the individual bed particles and pyrolyzing as a multitude of thin layers. 

Adjacent the ionomeric membrane on both sides are the catalyst layers (Fig. 1). As described above, these are platinum black/PTFE composites with high platinum loadings (typically 4 mg Pt/cm on each electrode) or composites of carbon-supported platinum and recast ionomer, with or without added PTFE, of much lower platinum loading (as low as 0.1 mg Pt/cm on each electrode). The electrochemical processes in the fuel cell take place at these electrocatalysts. In the hydrogen (or methanol reformate)/air fuel cell, the processes at the anode and cathode, respectively, are ... 

An alternative to filling or coating with a catalyst layer the microcharmels, with the related problems of avoiding maldistribution, which leads to a broad residence time distribution (RTD), is to create the microchannels between the void space left from a close packing of parallel filaments or wires. This novel MSR concept has been applied for the oxidative steam reforming of methanol [173]. Thin linear metallic wires, with diameters in the millimeter range, were close packed and introduced into a macro tubular reactor. The catalyst layer was grown on the external surface of these wires by thermal treatment. 

As far as the action of supported bimetallic catalysts is concerned, the main theories suggest either geometric and/or electronic effects to account for the improved catalytic properties. For instance, in platinum based naphtha reforming catalysts, the electronic modification of platinum particles may be induced by an interaction with an oxide layer of the promoter or by alloy formation. The electronic modification results in a change in the Pt-C bond strength of adsorp-... 

Above the catalyst are target brick and ceramic balls that protect the catalyst bed from excessive temperatures due to radiation from the oxygen burner [6]. The catalyst bed consists of two layers. The top layer is a high strength chrome-based catalyst which serves as a heat shield for the lower bed. The lower bed is a nickel-based reforming catalyst. 

TTie bayonet type of reformer tube is adopted to utilize the outlet process gas at the outlet of catalyst layer at the temperature of approximately 830 C. 

The temperature of process gas is lowered from 450°C to 600°C. to increase the heat input preventing carbon deposit. This design achieves heat input of 3.6MW from helium gas to the steam reformer and 1.2MW from outlet process gas of catalyst layer to inlet process gas. Total heat input of 4.8MW are utilized to heat up the process gas and to give steam reforming process heat. 

With a similar approach to decrease the distance between the wall or catalyst layer and the membrane surface drastically, all-metallic membrane modules with micromachined plates directly attached to the membrane have been fabricated by KIT [129]. Pd-alloy foils with different thicknesses ranging from 61 pm to 3 pm have been leak-tight integrated in the modules by laser welding (see Figure 7.11). This is considered a very practical approach and represents the first step towards the anticipated compact multi-layered microchannel membrane reformer system. 

Approaches for mass production of catalyst layers, i.e. reducing the coating cost are rarely reported. A cheap possibility has been demonstrated by O CormeU et al. (2011) by screen printing in the application of micro-engineered fuel reformers for hydrogen production. Such a coating is shown in Fig. 2. 

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