Washcoat impregnation

R 20] [P 3] In Figure 4.49 some experimental results are shown. The y-alumina washcoat impregnated with Cu/ZnO delivers a hydrogen yield of 78% at 98% selectivity. 

The electron-microscopic observation of the samples prepared showed the presence of nanosize particles (60—200 nm) which sometimes were accompanied by larger (1—10 pm) flake-like formations. The smaller particles form agglomerates which almost cover all the surface of the alumina washcoats. The total surface area of the washcoat, impregnated... 

In this work the catalytic activity of a series of copper oxide catalysts supported on monolithic honeycomb supports in the reduction of nitrogen oxide with propylene in an oxidising atmosphere was studied. The monoliths were produced from acid washed sepiolite, sepiolite or a mixture of sepiolite and alumina in order to study the effect of the support on the activities and selectivities of the catalysts. Tlie introduction of nickel oxide as a second active species on the overall activity was also detennined. Finally tlie application of an alumina washcoat impregnated with the copper and nickel salts to increase the accessibility of tlie gases to be treated to the active phase was studied. 

A desiccant wheel assembly consists of i) a core that contains the desiccant materials, ii) a core/wheel support structure, iii) a drive system to rotate the wheel at a very low speed, and iv) a set of air seals to separate the process air stream from the regeneration air stream. The core has a monolith honeycomb type structure. Both sinusoidal and hexagonal channels are used in commercial equipment. Various types of materials have been used for support matrix that includes ceramic, glass fibers, and corrugated aluminum sheets. The desiccant materials may be washcoated, impregnated, or formed in situ on the support matrix. 

Honeycombs made of different materials (cordierite, mulUte, muUite-zirconia, alumina, silicon carbide, yttrium-stabilized zirconia) have been supplied by CTI Company [8] as supports to prepare catalysts for lab-scale reactors. They present square channels and a total volume between 1 and 2 cm. The external shape can be parallelepiped or cylindrical. The preparation of square-shaped monoliths for H2O2 decomposition has been presented at the previous Catalyst Preparation Symposium [5], focusing on the influence of the washcoat procedure and the nature of the active phase on the catalytic activity. Figure 4-b displays one example of such catalysts, as received and after washcoating, impregnation and reduction steps. 

A washcoat, which provides a high surface area onto which the active catalyst is impregnated. The washcoat typically consists of a mixture of zirconium, cerium and aluminium oxides. Apart from providing high surface area the washcoat also acts as an oxygen storage system (see below). 

Fig. 16 can help visualize the location where the reaction is likely to take place based on the above discussion and calculations. While the entire washcoat is impregnated with catalyst, which must be done to achieve a robust support on the SCT, the calculations indicate the reaction will only take place at the surface sites near the top on the sketch and on the SEM. 

Washcoat High surface area oxide impregnated with catalytic species and bound to the walls in the channel of a monolithic structure. 

Aluminas are used in various catalytic applications, a-, y-, and -aluminas are all used as support materials, the first one in applications where low surface areas are desired, as in partial oxidation reactions. The latter two, and especially y-alumina, in applications where high surface areas and high thermal and mechanical stability are required. One of the most prominent applications of y-alumina as support is the catalytic converter for pollution control, where an alumina washcoat covers a monolithic support. The washcoat is impregnated with the catalytically active noble metals. Another major application area of high-surface aluminas as support is in the petrochemical industry in hydrotreating plants. Alumina-supported catalysts with Co, Ni, and/or Mo are used for this purpose. Also, all noble metals are available as supported catalysts based on aluminas. Such catalysts are used for hydrogenation reactions or sometimes oxidation reactions. If high... 

Figure 8 Steam reforming of hexane at flow rates of 2 0 and 0 64 Ib/hr of water and hexane, respectively Axial bed-temperature and composition profiles for a metal monolith (250 cells/in consisting of Kanthal support/7-Al203 washcoat/NiO catalyst, and a packed bed of Girdler G-9(X pellets (j in. X in ) of alumina impregnated with nickel. (From Ref. 9.)...

X 10 Alumina-washcoat steel-alloy support impregnated with nickel... 

Kim et al. [40] made an attempt to oxidize phenol in water solutions using a monolith reactor. Alumina-washcoated cordierite monoliths (62 celLs/cm ) impregnated with copper... 

Crynes et al. [41] continued the study of Kim et al. [40]. The novel monolithic froth reactor, with a monolithic section 0.42 m long and 5 cm in diameter, was used. Cordierite monoliths with a cell density of 62 cells/cm were stacked, one on top of another, to provide a structure 0.33 m long. The monoliths, washcoated with 7-alumina and impregnated with CuO, were tested at 383-423 K and 0.48-1.65 MPa. The liquid flow rate was varied from 0.4 to 3.5 cm sec", and the gas flow rate ranged from 15.8 to 50 cm sec". Phenol in a concentration of 5000 ppm was typically oxidized with air. The reaction rate versus the liquid flow rate showed a distinct maximum of approximately 2 mol g"t sec" at about 1.7 cm sec", while the dependence of the reaction rate on the gas flow rate was rather weak, with a tendency to decrease as the flow rate increased. 

Methods of catalysing the washcoat can be very simple ones of dipping the washcoated monolith in solutions of metal ions, but great care has to be taken to ensure that the bonding properties of the washcoat are not destroyed by the treatment. By far the best practice is to use the exchange properties of the washcoat material with suitable metal salt solutions. Once impregnated it is usually necessary to employ a thermal/reductive treatment to convert any precious-metal species to the metallic state. 

Ru impregnated y-Al203 catalyst was washcoated on cordierite monolith/ceramic forms and pellets. Among them, the Ru supported on ceramic foams exhibited better performance in the autothermal reforming of ethanol probably due to smaller pore size and higher tortuosity of the support. 

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