High Temperature Chemical Vapor Deposition defined

The nanotextural/structural and chemical properties of carbons determine their efficiency in electrochemical apphcation as electrodes. A strict control of the carbonization process (time, temperature, gas flow), the kind of natural or synthetic precursor and/or chemical vapor deposition conditions allow to prepare carbons with almost defined structure/nanotexture. Various advanced forms of carbon can be designed and prepared by a careful selection of templates, in such a way that one-, two-, or three-dimensional carbons can be easily obtained [9-12]. The modification of carbon by an activation process gives a further possibility of affecting the properties, especially by high developing of the specific surface area [13]. 

Physical vapor deposition with shadow masks is known for its simplicity for creating defined areas of thin-film catalytic material in microreactors. This technique was used to deposit silver in the reaction manifolds of microreactors for small-scale synthesis of valuable fine chemicals (Figure 1.4a). The manifolds consisted of a network of 16 parallel channels (19 mm x 600(im x 60-220 tm), in which the oxidative dehydrogenation of 3-methyl-2-buten-l-ol to aldehyde was carried out successfully for temperatures up to 464 °C [31]. The conversion increased smoothly with temperature and low oxygen and high alcohol concentrations were beneficial for selectivity, in addition to less deep channels (higher catalyst surface area to reaction channel volume). For temperatures >400°C, the selectivity deteriorated due to CO and CO2 formation. 

Most advanced techniques for coating a substrate with a nanomaterial layer are based on CVD and PVD techniques. In PVD techniques, in essence the source material is vaporized using simple evaporation or ion sputtering in a vacuum environment. In contrast to the PVD system, chemical reactions in gaseous phases are carried out at elevated temperature in CVD techniques. Generally, gas precursors react at a heated substrate to deposit a film or nanostructures. Despite the high cost, PVD and CVD techniques are employed in order to deposit highly pure and very defined films onto various substrates. 

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