Catalysts deposition techniques

A purchasable cross-flow heat exchanger for application in laboratory-, pilot- and production-scale plants was developed by FZK. By incorporation of a catalyst on the quadratic plates inside the heat exchanger, it can also be used as a catalytic wall reactor. Operating conditions up to 850 °C (stainless steel) and pressures of more than 100 bar are possible, and the specific inner surface area is up to 30 000 m m. The reactors can be obtained in many materials and three different sizes with a maximum flow of 6500kgh (water). Therefore, the reactors can be adjusted for various processes, and all types of catalyst deposition techniques are possible [111]. This reactor has already been applied to the catalytic oxidation of H2 by Janicke et al. [112], for example. 

One of the advantages of a comprehensive fuel cell model is that it allows for the assessment of the different loss mechanisms. This is shown in Figure 3.24. The most important loss mechanism is the activation overpotential at the cathode side, which has to be addressed with improved catalyst deposition techniques. Due to the transfer coefficient of = 0.5 ) for the... 

The conversion of protein-made nanostructnres, e.g., microtnbnles, into conducting nano-wires was also recently investigated [11] Metallization of microtnbnles, by an electrolyte nickel deposition technique, initiated by molecnlar palladinm catalysts, was described. 

The selective deposition technique seems a surface modification of oxides. In this regard, the modification of material surface is generally carried out in the field of the catalyst preparation. Catalysts are divided into heterogeneous and homogeneous catalysts. The former is well known to be used in the petroleum industry and almost all catalysts are solid, in particular, the supported catalysts. The supported catalysts are composed of the main... 

The palladium-tin catalysts were prepared by Engelhard on a commercial wood based carbon powder with a BET snrface area of approximately 800 m /g and a median particle size (D50) of 19 microns. The preferred carbon was chosen mainly for having good filtration properties. Catalysts with essentially equivalent activities for selectivity and conversion could also be made on two other similar carbons. The preparation process is proprietary but is based on the well-known adsorption-deposition technique (8). Reduction during the preparation process was accomplished via an Engelhard proprietary method. A series of catalysts containing from 1 to 7.5 wt% palladium and from 0 to 1 wt% tin were prepared by the same technique and provided for the experimental program. 

Platinum deposition techniques, 79 157 Platinum dichloride, 79 655 Platinum-divinyltetramethyldisiloxane complex, in silicone network preparation, 22 563 Platinum films, 79 658 Platinum gauze catalyst, 77 180-181 Platinum-group metal compounds, 79 635-667 analysis of, 79 637 economic aspects of, 79 635-636 health and safety factors related to, 79 658... 

Although the sputter deposition technique can provide a cheap and directly controlled deposition method, the performance of PEM fuel cells with sputtered CLs is still inferior to that of conventional ink-based fuel cells. In addition, other issues arise related to the physical properties of sputtered catalyst layers, such as low lateral electrical conductivity of the thin metallic films [96,108]. Furthermore, the smaller particle size of sputter-deposited Ft can hinder water transport because of the high resistance to water transport in a thick, dense, sputtered Ft layer [108]. Currently, the sputter deposition method is not considered an economically viable alternative for large-scale electrode fabrication [82] and further research is underway to improve methods. 

The characterization of the flow in existing DPF materials has been assessed by experiments and macroscopic continuum flow in porous media approaches. However, when it comes to material design it is essential to employ flow simulation techniques in geometrically realistic representations of DPF porous media. Some first applications were introduced in Konstandopoulos (2003) and Muntean et al. (2003) and this line of research is especially important for the development of new filter materials, the optimization of catalyst deposition inside the porous wall and for the design of gradient-functional filter microstructures where multiple functionalities in terms of particle separation and catalyst distribution (for combined gas and particle emission control) can be exploited. 

Takeuchi etal. (1985) have examined the HDS catalyst deposits in detail with XPS, ESR, x-ray diffraction, and electron microscopy. X-ray diffraction revealed the presence of the crystalline V3S4 phase, a nonstoichiomet-ric, polycrystalline solid with sulfur-to-vanadium ratios of 1.2 to 1.5. This polycrystalline material was observed by microscopy as 10-/um-long, rod-shaped crystals on the outer surface of the catalyst and about 0.1 /urn in length within the catalyst pores. The x-ray diffraction technique will not reveal any amorphous phases present. Electron spin resonance spectra revealed the presence of a vanadyl on the surface that was coordinated with 4S and distinctly different from the 4N coordination of the crude oil... 

Janicke et al. [63] applied a sol-gel-type deposition technique by filling micro channels with aluminum hydroxide solution, which was dried and caldned at 550 °C thereafter. Platinum was introduced as catalyst by impregnation on the coating up to three times, resulting in different loadings of the precious metal. 

Another specific feature of the catalytic behavior of the structures under study consists in that the chemical nature of a metal becomes a factor less important for catalysis as the surface nanoparticles density increases. This is well seen in Figure 15.14, which shows the results obtained in measurements of the activity of copper- and nickel-based catalysts in the reaction of carbon tetrachloride addition to olefins. Presented in this figure are the activities of catalysts prepared by laser electrodispersion and the conventional deposition techniques. Two important features are worth noting. First, the activity... 

However, in heterogeneous catalysis, metals are usually deposited on nonconducting supports such as alumina or silica. For such conditions electrochemical techniques cannot be used and the potential of the metallic particles is controlled by means of a supplementary redox system [8, 33]. Each particle behaves like a microelectrode and assumes the reversible equilibrium potential of the supplementary redox system in use. For example, with a platinum catalyst deposited on silica in an aqueous solution and in the presence of hydrogen, each particle of platinum takes the reversible potential of the equilibrium 2H+ + 2e H2, given by Nemst s law as... 

In many homogeneous catalyst-based industrial processes efficient recovery of the metal is essential for the commercial viability of the technology (see Section 1.4). This is especially true for noble metal-based homogeneous catalytic reactions. Apart from economic reasons spent catalyst recovery is also essential to prevent downstream problems, such as poisoning of other catalysts, deposition on process equipment, waste disposal, etc. Several different techniques are being followed industrially for the recovery of the catalyst from the reaction medium after the end of the reaction ... 

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