Monolith effect

F. Shiraishi, K. Kawakami, A. Tamura, S. Tsuruta, and K. Kusunoki, Continuous production of free gluconic acid by Gluconobacter suboxydans IFO 3290 immobilized by adsorption on ceramic honeycomb monolith Effect of reactor configuration of further oxidation of gluconic acid to kato-gluconic acid, AppL Microbiol. BiotechnoL 31(5-6) 445 (1989). 

Supported C03O4-CeO2 monoliths effect of preparation method and Pd-Pt promotion on the CO/CH4 oxidation activity... 

Xie SF, Svec F, Frechet JMJ. Preparation of porous hydrophilic monoliths Effect of the polymerization conditions on the porous properties of poly (acrylamide-co-N,N-meth-ylenebisacrylamide) monolithic rods. J. Polym. Sci. A 1997 35 1013-1021. 

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... 

A. Di Benedetto, F. S. Marra, F. Donsi, G. Russo, Transport phenomena in a catalytic monolith effect of the superficial reaction, AIChE J.. 2006, 52, 911-923. 

Figure 28.11. CO oxidation runs over copper monoliths effect of packaging on the T-difference between monohth axis and tube waU. Flow rate 7,000 cm /min (STP) CO feed 5% v/v. Toven 215°C (sample C), 200°C (sample E). Reprinted from Ref. 107. Copyright 2004 with permission from Elsevier.

Catalytic Unit. The catalytic unit consists of an activated coating layer spread uniformly on a monolithic substrate. The catalyst predominantly used in the United States and Canada is known as the three-way conversion (TWC) catalyst, because it destroys aU three types of regulated poUutants HC, CO, and NO. Between 1975 and the early 1980s, an oxidation catalyst was used. Its use declined with the development of the TWC catalyst. The TWC catalytic efficiency is shown in Figure 5. At temperatures of >300° C a TWC destroys HC, CO, and NO effectively when the air/fuel mixture is close to... 

D. W. Wendland, W. R. Matthes, and P. L. Sorrell, Effect of Header Truncation on Monolith Converter Emission Control Peformance, SAE 922340, Society of Automotive Engineers, Warrendale, Pa., 1992. 

The ceramic oxide carrier is bonded to the monolith by both chemical and physical means. The bonding differs for a ceramic monolith and a metallic monolith. Attrition is a physical loss of the carrier from the monolith from the surface shear effects caused by the exhaust gas, a sudden start-up or shutdown causing a thermal shock as a result of different coefficients of thermal expansion at the boundary between the carrier and the monolith, physical vibration of the cataly2ed honeycomb, or abrasion from particulates in the exhaust air (21) (see Fig. 6d). 

Monolithic refractory coatings have been applied to metallic components in furnaces for fuel ash corrosion control. Results have been less than satisfactory because of the large thermal expansion mismatch between the metal and refractory. Failure usually occurs upon thermal cycling which causes cracking, eventual spalling of the refractory, and direct exposure of the metal to the effects of the fuel ash. 

A sophisticated quantitative analysis of experimental data was performed by Voltz et al. (96). Their experiment was performed over commercially available platinum catalysts on pellets and monoliths, with temperatures and gaseous compositions simulating exhaust gases. They found that carbon monoxide, propylene, and nitric oxide all exhibit strong poisoning effects on all kinetic rates. Their data can be fitted by equations of the form ... 

Diffusion effects can be expected in reactions that are very rapid. A great deal of effort has been made to shorten the diffusion path, which increases the efficiency of the catalysts. Pellets are made with all the active ingredients concentrated on a thin peripheral shell and monoliths are made with very thin washcoats containing the noble metals. In order to convert 90% of the CO from the inlet stream at a residence time of no more than 0.01 sec, one needs a first-order kinetic rate constant of about 230 sec-1. When the catalytic activity is distributed uniformly through a porous pellet of 0.15 cm radius with a diffusion coefficient of 0.01 cm2/sec, one obtains a Thiele modulus y> = 22.7. This would yield an effectiveness factor of 0.132 for a spherical geometry, and an apparent kinetic rate constant of 30.3 sec-1 (106). 

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. 

Most of the NO reducing catalysts in pellet or monolithic form begin to lose their activity at 2000 miles and fail to be effective at 4000 miles. This lack of durability may well be connected to the usage of the NO bed for oxidation purposes during the cold start, which exposes the NOx catalysts to repeated oxidation-reduction cycles. Better catalyst durability can be anticipated in the single bed redox catalyst with a tightly controlled air-to-fuel ratio, since this oxidation-reduction cycle would not take place. Recent data indicates that the all metal catalysts of Questor and Gould may be able to last 25,000 miles. 

The role of the matrix is to protect the filler from corrosive action of the enviroment and to ensure interactions between the fibers by mechanical, physical and chemical effects. The mechanical properties of fiber composites are dependent on the mutual position of the fibers in the monolithic materials. 

---