Cordierite monoliths

Two types of catalytic converters are currently being used for meeting the passenger car emission standards in the U.S. three-way converters and dualbed converters. Both converters contain three-way catalysts, but with the dual-bed converter the three-way catalyst is followed by an air injection/ oxidation catalyst system. As for the earlier oxidation catalysts two forms of catalyst support are used pellets (thermally stable transitional alumina) and monoliths (cordierite honeycombs coated with a thin alumina washcoat). Figure 7 shows four catalytic converters currently being used by General Motors. 

The work presented in this paper is the first part of a project aiming at the development of tailor-made oxidation catalysts for diesel engines fuelled by alcohol fuels, ethanol or methanol. The investigation is focused on the influence of support material on the low temperature oxidation of ethanol and acetaldehyde. The study presents results from an experimental investigation with precious metal catalysts applied on monolithic cordierite substrates. Platinum or palladium were applied onto a support consisting of either aluminum oxide, cerium dioxide, silicon dioxide or titanium dioxide. 

Catalysts were prepared by impregnating the noble metal chloride onto either an alumina washcoat or a proprietary washcoat containing alumina, ceria and other base metals. The catalyst was supported on a monolithic cordierite substrate with 64 square cells/cm. Cylindrical cores used for laboratory evaluations were 2.5 cm in diameter and, unless otherwise noted, 5 cm in length. The length of each core was composed of smaller segments taken from various locations down the monolith bed in order to minimize sampling biases. 

A parametric study on the effects of axial heat conduction in the solid matrix has shown that i) such effects are negligible in ceramic monoliths (cordierite, kj = 1.4 w/m/K) but expectedly significant in metallic monoliths (Fecralloy, k i = 35 W/m/K) when a constant heat flux is imposed at the external matrix wall ii) however, the influence of axial conduction in metallic monoliths is much less apparent if a constant wall temperature condition is applied, since the monolith tends to an isothermal behavior. Metallic matrices exhibit very flat axial and radial temperature profiles, which seems promising for their use as catalyst supports in non-adiabatic chemical reactors. 

Figure 3 - Effect of cell density and of channel size on heat transfer efficiency of a monolith with constant external wall temperature = 500 K. Case of ceramic monolith (Cordierite). Gas=air.

A ceramic monolith catalyst support, cordierite, consisting of silica, alumina and magnesium oxide. The purpose of this is to provide support, strength and stability over a wide temperature range. 

Two ways to reduce the diffusion length in TBRs are 1) use of smaller catalyst particles, or 2) use of an egg-shell catalyst. The first remedy, however, will increase pressure drop until it becomes unacceptable, and the second reduces the catalyst load in the reaction zone, making the loads of the TBR and the MR comparable. For instance, the volumetric catalyst load for a bed of 1 mm spherical particles with a 0.1 mm thick layer of active material is 0.27. The corresponding load for a monolithic catalyst made from a commercial cordierite structure (square cells, 400 cpsi, wall thickness 0.15 mm), also with a 0.1 mm thick layer of active material, is 0.25. 

The object was an auto exhaust catalyst, a monolith cylinder 25 mm in length and 38 mm in diameter. The outside wall was broken away so that one of the 1 ram-wide channels became accessible to the IR and probe laser beams, and a portion of one channel was studied in the manner shown schematically in the insert of Fig. 8. The sample was examined in air, because a cell large enough to contain the monolith was not available. The spectrum shows the features of cordierite [20], the material from which honeycomb monoliths are usually made, a broad absorption in... 

The cordierite extruded monoliths, having 400 square cellsAn, were similar to those used in automobile catalytic converters. However, instead of using an alumina washcoat as in the catalytic converter, these catalyst supports were loaded directly with 12 to 14 wt.% Pt in the same manner as the foam monoliths. Because these extruded monoliths consist of several straight, parallel channels, the flow in these monoliths is laminar (with entrance effects) at the flow rates studied. 

The monolithic stirrer reactor (MSR, Figure 2), in which monoliths are used as stirrer blades, is a new reactor type for heterogeneously catalyzed liquid and gas-liquid reactions (6). This reactor is thought to be especially useful in the production of fine chemicals and in biochemistry and biotechnology. In this work, we use cordierite monoliths as stirrer blades for enzyme-catalyzed reactions. Conventional enzyme carriers, including chitosan, polyethylenimine and different are used to functionalize the monoliths. Lipase was... 

Figure 11 Yields of H2, CO, CO2, and CH4 from reforming of benchmark gasoline fuel catalyzed by Rh- or Pt-CGO supported on a cordierite monolith (Conditions OjC = 0.88, SIC = 1.6, GHSV = 9,000...

Figure 1 Monolithic structures of various shapes. Square-channel cordierite structures (1, 3, 5, 6), internally finned channels (2), washcoated steel monolith (4).

Figure 2.88 CO conversion found for low-temperature water-gas shift at various reaction temperature vs. modified residence time (catalyst weight/carbon monoxide flow). Results from a micro channel stack reactor (closed symbols) are compared with conventional cordierite monoliths (open symbols) [82].

Germani et al. [82] compared the performance of their catalyst coating developed for water-gas shift in a micro structured reactor with that of the same catalyst coated on a cordierite monolith under identical reaction conditions. Higher conversion was achieved in the micro channels at same modified residence time under all experimental conditions applied. Figure 2.88 shows the CO conversion vs. a modified residence time (catalyst weight/flow of carbon monoxide) measured at various reaction temperatures. 

For the control of carbon monoxide, hydrocarbon, and nitrogen oxide emissions from automobiles, oval-shaped extruded cordierite or metal monolith catalysts are wrapped in ceramic wool and placed inside a stainless steel casing (Fig. 19-18a). The catalytic metals are Pt-Rh or Pd-Rh, or combinations. Cell sizes typically ranges between 400 and 600 cells per square inch. The catalysts achieve over 90 percent reduction in all three pollutants. 

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