Monoliths alumina washcoated

If the same quantity of active ingredient is concentrated in an outside shell of thickness 0.015 cm, one obtains y> = 2.27. This would yield an effectiveness factor of 0.431 in a slab geometry, and the apparent kinetic constant has risen to 99.2 sec-1. If the active ingredient is further concentrated in a shell of 0.0025 cm, one obtains y> = 0.38, an effectiveness factor of 0.957, and an apparent kinetic constant of 220 sec-1. These calculations are comparable to the data given in Fig. 15. This analysis applies just as well to the monolith, where the highly porous alumina washcoat should not be thicker than 0.001 in. 

Table 3.9. shows the results of barometric hydrogen chemisorption on Cu/AlaOj, Ni/A Oj, Pt/Al203 and a Ni on alumina-washcoated monolith. 

Lenz and Aicher reported the experimental results obtained with an autothermal reformer fed with desulfurized kerosene employing a metallic monolith coated with alumina washcoat supporting precious metal catalysts (Pt and Rh) [78]. The experiments were performed at steam-to-carbon ratios S/C = 1.5-2.5 and... 

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. 

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... 

Temperature control was demonstrated in a series of experimental tests [8-10]. In one series of tests, both ceramic and metal honeycomb monolith supports were used [8,9]. The ceramic supports used in these tests were 46.5-cells/cm (square cells) Celcor monoliths 6.2 cm in diameter and 10.2 cm long, whereas the metal honeycomb monolith supports (made of Kanthal, a high-temperature alloy) had 38.8 cells/cm (hexagonal cells) and were 6.3 cm in diameter and 5.1 cm long. The ceramic and metal monoliths were washcoated with gamma alumina, and the nickel catalyst loadings were 13 and 5.6% (average), respectively. In comparison, the conventional catalyst used for reference was... 

The application of monolith catalysts to a variety of commercial synthesis processes has been investigated because of the potentially smaller size and lower pressure drop through the chemical reactors. One of the earliest of these investigations was for methanation, the chemical reaction between carbon monoxide and hydrogen to produce methane selectively. In a detailed study [14] a comparative evaluation involved the use of nickel catalyst on (1) spherical alumina pellets (0.32-cm diameter), (2) alumina washcoated (10-20% by weight) cordierite monoliths with 31- and 46-cells (square)/cm density, (3) an alumina... 

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... 

Alumina washcoating is taken as an example to illustrate the washcoating of an alumina layer onto a monolith surface. 

Figure 1 shows the block scheme of washcoating. A dry monolith is dipped in an Al-sol. Afterwards, it is drained or blown with air to remove the remaining sol. After drying and calcination at appropriate temperatures, the alumina washcoating is completed. 

Carbon coating can be achieved using pyrolysis of hydrocarbons at elevated temperatures [69]. Figure 2 shows a device used for carbon coating via hydrocarbon pyrolysis. In the example described here, an alumina-washcoated monolith is covered with carbon by pyrolysis of cyclohexene. A gas mixture of cyclohexene in nitrogen is passing the reactor at a certain flow rate. The monolith block to be coated is placed in the middle of the heated tubular reactor. The reaction takes place at 873-973 K, and the amount of carbon deposited can be controlled by the temperature and the time on stream. Up to 3-10 wt% carbon can be homogeneously coated onto the monolith in this way. It appears that the surface area of the carbon-coated alumina-washcoated cordierite monolith is of... 

Our preliminary results of nickel on carbon-coated monolithic catalysts show that in a hydrogenation reaction it is five times more active than the corresponding nickel on alumina-washcoated monolithic catalyst without carbon coating. 

Monoliths made of metal foils can also be used as substrates in combustion catalysts [19, 20]. The metal is generally an iron- or nickel-based steel containing small amounts of aluminum. The aluminum diffuses to the surface on heating and oxidizes to form an adherent alumina layer. This alumina layer gives the alloy high oxidation resistance and is essentially self-healing as it arises from diffusion from the bulk material. It also provides good adhesion for the alumina washcoat. 

Cordierite monoliths were coated with an alumina washcoat and stabilised at 550°C. Some of the samples were then immersed in either an aqueous solution of cerous or cobalt nitrate, dried and calcined in air at 550°C at which the metal nitrates decomposed into their oxides [11]. The samples were weighed and the procedure was repeated until 40 mg of the metal oxide had been deposited onto the alumina washcoated monolith samples. Pt and Pd were applied by direct impregnation using aqueous solutions of HaPtCla and PdCb followed by diying and calcination in air at 550°C [8]. The Pt and Pd loadings (2.0 and 1.09 mg, respectively) of the catalysts were equal on molar basis. The nominal composition of the eight catalysts prepared are listed in Table 1. 

Porous and thermally stable washcoating layer on mechanically strong support is an important component in both oxidative and three-way catalysts used for car exhaust gas cleaning. The washcoat provides a high and stable surface area for dispersion of the active component of the catalysts consisting of platinum and /or paladium. Usually for the preparation of this layer aluminas modified by La, Ce, Zr, Si etc. are used [1-3]. As it was shown in [4-6] the properties of modified aluminas depend on the method of introduction of the additives In this work we present the results on the preparation and study of model alumina systems modified by La, Ce and Zr as well as of monolith supports washcoated by optimal compositions of alumina and additives. 

Flow reactor studies were performed using monolith samples with an alumina washcoat, a storage compound (BaO) and noble metals (Pt, Rh). In order to elucidate the importance of the various ingredients, samples were also prepared without storage compoimd or noble metals, respectively. For the FTIR studies, similar powder catalysts were pressed into thin discs. 

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. 

Ceramic monoliths have proven themselves effective as substrates for catalyst washcoat and precious metal because they provide a relatively uniform porous surface. In the catalyst application process, the amount of alumina washcoat picked up depends upon the total porosity, as well as, the size distribution and shape of the pores within the wall. Likewise, the amount of precious metal picked up depends largely upon the amount of porous washcoat on the substrate. Catalyst coaters, therefore, have learned to optimize their process around typical properties of the substrate. However, through subtle variances in raw materials and process steps, variances in porosity occur piece to piece and lot to lot. 

Figure 2 - SE micrograplis of cordierite monoliths with two layers of a-alumina washcoat and one of y-alumina a) longitudinal view of the channels b) transversal view of the channels c) detail of one comer d) detail of the two last layers.

Table 1. BET surface area (m /g) of monolithic catalysts. The specific surface area of the bare cordierite, ceria-alumina washcoat and Co30Ce powder are also...

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. 

The incorporation of the active phases on to the monolithic support after first applying an alumina washcoat greatly increased the selectivity of the catalyst where NO conversions of 75% could be achieved. This was probably due to a reduction in any diffiisional limitations. 

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. 

Villegas L, Masset F, Guilhaume N (2007) Wet impregnation of alumina-washcoated monoliths effect of the drying procedure on Ni distribution and on autothermal reforming activity. Appl Catal A 320 43-55... 

Rodrigues, CP, Schmal, M. Nickel-alumina washcoating on monoliths for the partial oxidation of ethanol to hydrogen production. Int J. Hydrog. Energy 2011 36 10709-10718. 

Alumina washcoating and metal deposition of ceramic monoliths... 

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