Washcoat monoliths

Figure 10.5. Monolith, washcoat and noble metal particles in an automotive exhaust catalyst.

There are two major types of diffusion contributing to mass transport in the monolith washcoat (cf., e.g. Aris, 1975 Froment and Bischoff, 1979, 1990 Poling et al., 2001) volume (molecular) diffusion, Eq. (14), and Knudsen diffusion, Eq. (15), the latter one being dominant in small pores. 

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. 

This project ends March 31, 2003. Plans for the remainder of the project include scale-up of the monolith washcoating process and testing of a 10-kW scale monolith at HydrogenSource. 

Figure 7. Estimated cost and platinum content of a WGS monolith washcoated with PEceria catalysts.

Typical monolithic washcoats are composed of support materials to disperse the catalytic component and additives to stabilize and promote their flmction. The Strategic Material Architecture concept builds on the premise that each particular catalytic function within the washcoat is surrounded by its own optimum environment to enhance a particular reaction. Application of the washcoat to the... 

The lean NOx reduction by CH4 in the presenee of 10-15% water vapor was studied on bi-and tri-metallic powder catalysts containing two or three of the following species Co, Pd, Ce, and Pt on HMOR. A cooperative effect in the Pd-Co, Pd-Ce, Pd-Ce-Co and Pd-Pt-Ce systems was found for CFI4-SCR under wet conditions. Pd-Ce/HMOR and Pd-Ce/Co-HMOR catalysts were more tolerant to the coexistence of H2O and SO2 in the gas feed than Pd/Co-HMOR. Co, Pd and Ce species were impregnated on ceramic monoliths washcoated with mordenite. The results of NOx reduction were different for the monolithic and powdered catalysts. However, a similar trend in the CH4-SCR activity of both catalyst types was observed. 

Precision Combustion Catalytica, TKK KK and Ib, fully catalytic Ila, hybrid, partial inactive catalyst Recuperative small-scale Gasoline or JET Natural gas Advanced Technology Surface Reactor Detailed composition is proprietary, 2-3 stages FeCrAl-metal monolith washcoated with metal oxide, first stage Pd Atm + Ultra-short channels yield low emissions, low pressure drop and good fuel efficiency + Prevent catalyst overtemperature, no second mixing —Control of post-catalytic autoignition delay time 19 15, 176, 177... 

Zhang E, Hayes RE, Kolaczkowski ST. A new technique to measure the effective diffusivity in a catalytic monolith washcoat. Chemical Engineering Research and Design 2004 82 481-489. 

Deposition precipitation method was found suitable to obtain a homogeneous distribution of nickel on monolith washcoated with alumina. Drying in a microwave oven is helpful in maintaining a homr eneous metal dispersion over the monolith. 

The dual-layer ASC system herein studied consisted of commercial state-of-the-art PGM and SCR catalysts the PGM catalyst was a Pt/Al203-based system, while an Fe-zeolite was used as the NH3-SCR catalyst component. The original ASC monolith was a dual-layer system with an SCR layer coated on top of a PGM one. For the present study, in addition to the dual-layer monolith, the SCR and PGM catalysts were supplied both in the form of precursor powders of the monolith washcoat and in the form of single washcoated monoliths (400 CPSI, wall thickness = 5 mils). 

Step 3, monolith washcoating. The monoliths are put into the sol for 1 h with careful control of the temperature and viscosity. Then, they are retrieved and the channels are flushed with a smooth argon flow before drying and thermal treatment. Up to three successive washcoat stages can be carried out to get a given porous wash-coat content. 

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