Poisoning mechanism

J. R. Poison, Mechanical Pressing of Explosives, Iowa Army Ammunition Plant, Burlington, Iowa, 1973. 

Not only 02 molecules but also other groups can be bound to the iron atom of hemoglobin. Specifically, carbon monoxide molecules can be so attached and, in fact, CO is more firmly bound to hemoglobin than is O2. This is one detail of the carbon monoxide poisoning mechanism. If we breathe a mixture of CO and 02 molecules, the CO molecules are preferentially picked up by the red blood cells. Since the sites... 

It was shown in laboratory studies that methanation activity increases with increasing nickel content of the catalyst but decreases with increasing catalyst particle size. Increasing the steam-to-gas ratio of the feed gas results in increased carbon monoxide shift conversion but does not affect the rate of methanation. Trace impurities in the process gas such as H2S and HCl poison the catalyst. The poisoning mechanism differs because the sulfur remains on the catalyst while the chloride does not. Hydrocarbons at low concentrations do not affect methanation activity significantly, and they reform into methane at higher levels, hydrocarbons inhibit methanation and can result in carbon deposition. A pore diffusion kinetic system was adopted which correlates the laboratory data and defines the rate of reaction. 

Olson KR Carbon monoxide poisoning Mechanisms, presentation, and controversies in management. J Emerg Med 1 233-243, 1984... 

Bajgar J (2004) Organophosphates/nerve agent poisoning mechanism of action, diagnosis, prophylaxis, and treatment. Adv Clin Chem 38 151-216... 

Jacobsen D, Mcmartin KE. Methanol and ethylene glycol poisonings. Mechanism of toxicity, clinical course, diagnosis and treatment. Med Toxicol 1986 1 309. 

Cooper, B. J., Renny, L. V., and White, R. J., Lead Poisoning of Automobile Emission Control Catalysts—Influence of Emission System and Catalyst Design Characteristics on the Poisoning Mechanism, Am. Chem. Soc.. Symp. Automot. Catal., Chicago Meet., 1975. 

The origins of modem toxicology can be traced to M.J.B. Orfila (1787-1853), a Spaniard bom on the island of Minorca. In 1815 Orfila published a classic book,1 the first ever devoted to the harmful effects of chemicals on organisms. This work discussed many aspects of toxicology recognized as valid today. Included are the relationships between the demonstrated presence of a chemical in the body and observed symptoms of poisoning, mechanisms by which chemicals are eliminated from the body, and treatment of poisoning with antidotes. 

The bifurcation diagram in the U/I parameter plane of this adsorption/reaction mechanism, which was designated subclass 1, is the same as the one of the above discussed reaction-poison mechanism that forms subclass 2. 

In order to investigate the poisoning mechanism, the FT-IR spectra were measured for the platinum powder before and after exposed to the vapor of HN03 aqueous solution. A sharp peak which belongs to N03 characteristic absorption was observed at 1390 cm 1 as shown in Fig.3. The formation of some platinum nitrate compounds seems quite unlikely under the present experimental condition, We might conclude from these results that the poisoning was caused by the reversible adsorption of HN03 on the Pt catalyst surface. 

What are the rates of sulfur adsorption and of sulfur poisoning and can they be predicted Can catalyst life in commercial catalyst applications be predicted based on poisoning mechanisms and models ... 

Poisoning of iron catalysts during ammonia synthesis by sulfur compounds has received relatively little attention (154, 240-244). Nevertheless, the previous work provides information on the poisoning mechanism and interesting examples of how oxide promoters may influence the sulfur poisoning behavior of a catalytic metal. 

Fig. 7.7. Idealized poisoning mechanism (a) sintering of the catalytic components, (b) sintering of the carrier, (c) selective poisoning, and (d) nonselective poisoning.

One interesting example of different selective poisoning mechanisms is that of S03 deactivation of Pt on A1203 used for abating emissions from combustion reactions. The Pt oxidizes the S02 to S03 and the latter adsorbs onto the A1203 forming a sulfate. Slowly the carrier surface becomes so sul fated that it occludes the Pt within the pores and the cata-... 

Scheme 3 shows the accepted poisoning mechanism for grafted silica systems in our model reaction. This is characterised by amide and nitrile bands in the infra-red spectrum of used catalysts which cannot be displaced by washing. We have also produced a similar spectrum by refluxing fresh catalyst with ethyl cyanoacetate and, as expected, the treated material is not active if used in a model reaction. 

Catalyst deactivation is assumed to take place by a poisoning mechanism only. The deactivation of catalyst by thiophene will serve as a model deactivation reaction. Weng et al. (40 analyzed the deactivation data and proposed a rate equation, linear in concentration of poison, x, and activity 0 ... 

The last assumption is referred to as the quasi-steady-state assumption. The fraction of the bed which is poisoned is a function of time only and not of bed length, reactor space time, or the concentration of the reactant A external to the pellets. At any given time the bed activity will be constant, and only one concentration of the poison precursor species S will exist in the bed. Such a situation will be more likely to occur when deactivation rates are low compared to reaction rates. Under this condition S will spread evenly throughout the bed. Within particles, however, concentration gradients of S may still exist depending on the poisoning mechanism and the pore and pellet properties. 

Camara, G.A. et al.. The CO poisoning mechanism of the hydrogen oxidation reaction in proton exchange membrane fuel cells, J. Electrochem. Soc., 149, A748, 2002. 

Figure 1.11 Rates of polymerization with transition metal catalysts may be quite different because of accessibility of active centers, presence of poisons, mechanism of activation, etc. Kinetic profile must be accommodated by process conditions (see Chapter 7).

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