Monolith honeycomb

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... 

Ceramem Ceramics oxides Coerdierite 0.05-0.5/im Honeycomb monolith 1.8... 

The structural elements of commercial inorganic membranes exist in three major geometries disk, tube or tube bundle, and multichannel or honeycomb monolith. The disks are primarily used in laboratories where small-scale separation or purification needs arise and the membrane filtration is often performed in the flow-through mode. The majority of industrial applications require large filtration areas (20 to over 200m ) and, therefore, the tube/tube bundle and the multichannel monolithic forms, particularly the latter, predominate. They are almost exclusively operated in the cross-flow mode. 

The SCR catalysts are used in the form of honeycomb monoliths or plates to guarantee low pressure drops in view oflarge frontal area with parallel channels, high external surface area per unit volume of catalyst, high attrition resistance and low tendency for fly ash plugging. The SCR monoliths and plates are assembled into standard modules and inserted into the reactor to form catalyst layers. 

Tronconi et al. [46] developed a fully transient two-phase 1D + 1D mathematical model of an SCR honeycomb monolith reactor, where the intrinsic kinetics determined over the powdered SCR catalyst were incorporated, and which also accounts for intra-porous diffusion within the catalyst substrate. Accordingly, the model is able to simulate both coated and bulk extruded catalysts. The model was validated successfully against laboratory data obtained over SCR monolith catalyst samples during transients associated with start-up (ammonia injection), shut-down (ammonia... 

The catalyst, used in the form of a ceramic honeycomb monolith, is constituted, as in mobile applications, by a noble metal and an absorber element, such as potassium, deposited on a Y-AI2O3 wash-coat layer. In the oxidation and absorption cycle, the SCON Ox catalyst works by simultaneously oxidizing CO and UHCs to CO2 and H2O, while NOj, are captured on the adsorber compound. Catalyst regeneration is accomplished by passing a controlled mixture of regeneration gases across the surface of the catalyst in the absence of oxygen. 

Ceramic honeycomb monoliths are porous macro-structured supports consisting of parallel channels. On the walls a thin layer of active material can be applied (Figure 1). Honeycomb catalyst supports were originally developed for use in automotive... 

Since 1981, three-way catalytic systems have been standard in new cars sold in North America.6,280 These systems consist of platinum, palladium, and rhodium catalysts dispersed on an activated alumina layer ( wash-coat ) on a ceramic honeycomb monolith the Pt and Pd serve primarily to catalyze oxidation of the CO and hydrocarbons, and the Rh to catalyze reduction of the NO. These converters operate with a near-stoichiometric air-fuel mix at 400-600 °C higher temperatures may cause the Rh to react with the washcoat. In some designs, the catalyst bed is electrically heated at start-up to avoid the problem of temporarily excessive CO emissions from a cold catalyst. Zeolite-type catalysts containing bound metal atoms or ions (e.g., Cu/ZSM-5) have been proposed as alternatives to systems based on precious metals. 

In subsequent stages validation experiments were performed over monolith catalyst samples at two different scales (i) monolith core samples (up to 10 cm3) in a laboratory rig for integral reactor experiments and (ii) full-scale honeycomb monoliths (up to 43 L in size) in engine test bench runs. 

A variety of photocatalyst supports has been examined experimentally. Dip-coated glass slides or plates have been used in many experimental systems as a simple lab-scale supported photocatalyst system. Coated glass offers many of tlte important features of a supported photocatalyst while still offering relatively simple preparation. Honeycomb monoliths, widely used as commercial catalyst supports for a variety of gas-phase applications, have also been examined as photocatalyst supports (Fig. 3). Although these monoliths offer good stability and excellent throughput, providing illumination for the photocatalyst inside the monolith channels can be problematic [41,42]. Randomly structured support materials, like fiber-based filters, reticulated foams, and similar materials, have been used... 

Fig. 13.12 Opposed-flow diffusion flame between parallel, axisymmetric, burner faces that are fabricated as honeycomb monoliths. As illustrated, the flame is positioned on the oxidizer side of the stagnation plane. However, depending on the flow conditions as well as the fuel and oxidizer composition, the flame may form on the fuel side of the stagnation plane.

Fig. 17.18 Illustration of a catalytic honeycomb monolith and an enlarged view of the singlechannel model problem. In the model problem, the channel diameter (d = 2 mm) is much smaller than the channel length (L = 100 mm). For clarity, the illustration shows a large channel diameter.

The dynamic adsorption behaviour of volatile organic compounds on activated carbon honeycomb monoliths... 

Commercially available ACs were conformed as honeycomb monoliths with a magnesium silicate clay as binder. The textural and mechemical properties of the raw materials and the monolith composites were determined. These results were analysed together with the dynamic adsorption capacities towards o-dichlorobenzene (o-DCB) a chlorinated probe molecule used to simulate a dioxin. With this data, criteria by which the dynamic adsorption capacity could be related to the textural properties of the adsorption imits were established. 

Key words Activated carbon. Gas purification. Honeycomb monolith, VOCs. 

All the monolith composites were prepared at a 1 1 ratio between the magnesium silicate clay binder and the AC or alumina. After premixing of the dry powders by careful addition of water a dough was formed. This dough was extruded as honeycomb monolithic structures with parallel channels of square section at a cell density of 8 cells cm and a wall thickness of 0.9 mm using a Bonnot single screw extruder. 

The honeycomb monoliths were dried at room temperature and then heated in air to 150°C for 4h. Samples of each composite were also heat-treated at 500°C or 850°C in nitrogen. Heat-treatment in an inert atmosphere was necessary to avoid oxidation of the AC. These materials were subsequently used in all of the characterisation techniques and adsorption performance tests. 

One of the potentially wide-spread applications under development is catalytic filters for air pollution control. This combines separation and catalytic oxidation into one unit operation. One possibility is the oxidation of volatile organic carbon (VOC) by employing a porous honeycomb monolithic ceramic membrane filter. Inside the pores are deposited an oxidation catalyst such as precious metals. The resulting VOC removal efficiency can exceed 99% [Bishop et al., 1994]. 

Membranes that arc catalytically active or impregnated with catalyst do not suffer from any potential catalyst loss or attrition as much as other membrane reactor configurations. This and the above advantage have the implication that the former requires a lower catalyst concentration per unit volume than the latter. It should be mentioned that the catalyst concentration per unit volume can be further increased by selecting a high "packing density" (surface area per unit volume) membrane element such as a honeycomb monolith or hollow fiber shape. 

Due to their high stiffness and brittleness, it is not possible to extend to ceramic membranes geometries applicable with organic membranes like spirals, which give rise to high surface volume ratios. The ceramic membranes used for tangential filtration are nsually multichannel tubes or, in some applications, honeycomb monoliths. A very attractive type of membrane is the ceramic hollow fiber with an external diameter of less than 1 mm and ceramic walls with a thickness of a... 

The substrate is an integral part of the catalytic converter system. Its primary function is to bring the active catalyst into maximum effective exposure with the exhaust gases. In addition, it must withstand a variety of severe operating conditions, namely, rapid changes in temperature, gas pulsations from the engine, chassis vibrations, and road shocks. As noted earlier, pellets of cylindrical and spherical geometry and honeycomb monoliths both became available for catalyst supports. 

The original SCR catalysts were offered in the form of pellets or spheres and used in clean or low-dust applications. They were soon replaced by parallel-flow catalysts, namely, honeycomb monoliths, plates, and coated metal monoliths, as shown in Fig. 2. In the case of the SCR process, the main advantages of monolith-shaped catalysts with respect to conventional packed beds are as follows ... 

Selective catalytic reduction honeycomb monoliths (typically characterized by a square channel section) are obtained by extruding a mass of pastelike catalytic material. The ele-... 

Figure 2 Types of monolithic SCR catalysts (a) honeycomb monolith (b) plate-type catalyst (c) coated metal monolith.

Catalytic Fuel Combustion in Honeycomb Monolith Reactors... 

III. DESIGN OF HONEYCOMB MONOLITH COMBUSTION CATALYSTS A. Pros and Cons of Catalysis at High Temperatures... 

IV. PRACTICAL APPLICATIONS OF HONEYCOMB MONOLITHS IN CATALYTIC COMBUSTORS... 

There are three important outstanding issues that need concerted R D. The first issue is the further development of materials with thermal stability under combustion condition at the high temperatures prevailing in a gas turbine combustion chamber. Promising materials have been developed, but none fulfills the demand of a lifespan of at least 1 year. Besides, the most promising materials, such as the family of the hexa-aluminates, must be available in a honeycomb monolith shape, either as washcoat or directly extruded. Much work still needs to be done to optimize the preparation of monolithic thermostable catalysts. 

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