Ceramic honeycomb monolith

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. 

O. Ariga, M. Kimura, M. Taya, and T. Kobayashi, Kinetic evaluation and characterization of ceramic honeycomb-monolith bioreactor, J. Ferment. Technol. 64(4)321 (1986). 

F. Shiraishi, K. Kawakami, S. Kono, A. Tamura, S. Tsuruta, and K. Kusunoki, Characterization of production of free gluconic acid by gluconobacter suboxydans adsorbed on ceramic honeycomb monolith, BiotechnoL Bioeng, 33(11 ) 4 3 (1989). 

The introduction of automobile exhaust catalysts in the United States and elsewhere has produced a major market for platinum-type oxidation and reduction systems. An innovative consequence of this industry has been the development of ceramic honeycombed monoliths as catalyst supports. These structures contain long, parallel channels of less than 0.1 mm in diameter, with about SO channels per square centimeter. The monolith is composed of cordierite (2MgO - 2AI2O) SSiOj) and is manufactured by extrusion. A wash coat of stabilized alumina is administered prior to deposition of the active metal, either by adsorption or impregnation methods. 

Optimal thermostable composition of alumina and additives were chosen for using as a washcoat on cordierite and cilumosilicate ceramic honeycomb monoliths. 

Modify Pt/ceria catalyst suspensions with surfactants and binders, and washcoat catalysts onto ceramic honeycomb monoliths. 

Ciambelli P, Palma V, Palo E (2008) Comparison of ceramic honeycomb monolith and foam as Ni catalyst carrier for methane autothermal reforming. Catal Today. Catal Today 155 92-100... 

Lenz et al. [73] described the development of a 3 kW monolithic steam-supported partial oxidation reactor for jet fuel, which was developed to supply a solid oxide fuel cell (SOFC). The prototype reactor was composed of a ceramic honeycomb monolith (400 cpsi) operated between 950 C at the reactor inlet and 700°C at the reactor outlet [74]. The radial temperature gradient amoimted to 50 K which was attributed to inhomogeneous mixing at the reactor inlet. The feed composition corresponded to S/C ratio of 1.75 and O/C ratio of 1.0 at 50 000 h GHSV. Under these conditions, about 12 vol.% of each carbon monoxide and carbon dioxide were detected in the reformate, while methane was below the detection limit. Later, Lenz et al. [74] described a combination of three monolithic reactors coated with platinum/rhodium catalyst switched in series for jet fuel autothermal reforming. An optimum S/C ratio of 1.5 and an optimum O/C ratio of 0.83 were determined. Under these conditions 78.5% efficiency at 50 000 h GHSV was achieved. The conversion did not exceed 92.5%. In the product of these... 

Until recently the use of monolithic catalysts in non-adiabatic reactors was regarded as unfeasible due to poor radial heat transfer properties. Indeed, ceramic honeycomb monoliths are made of essentially insulating materials a theoretical analysis by Cybulski and Moulijn provided evidence that commercial monolith structures consisting of corrugated metal sheets exhibit modest heat transfer performances too. 

Shiraishi F, Kawakami K, Kono S, Tamura A (1989a) Continuous production of free gluconic acid by Gluconobacter suboxydans IFO 3290 immobilized by adsorption on ceramic honeycomb monolith effect of reactor configuration on further oxidation of gluconic acid to ketogluconic acid. Appl Microbiol Biotechnol 31 445-447... 

Utilization of porous ceramic honeycomb monoliths could realize large networks of microcharmel membranes for gas separation with superior mechanical stability. By increasing the thickness of the membrane... 

Keywords cellular ceramics, honeycomb monoliths, propulsion, energetic compounds... 

---