Poisoning of hydrogenation

Wang D-X, et al. 1989. [A review of 152 cases of acute poisoning of hydrogen sulfide.] ChinJPrev Med 23 330-332. (Chinese)... 

Although oxygon poisoning of hydrogenation at room temperature appears to... 

Alkene hydrogenation was also suggested to test for mass transfer effects during liquid-phase hydrogenations236,237. The method is based on the linear poisoning of hydrogen addition to alkenes (cyclohexene and apopinene) by CS2. When the active sites of Pd or Pt catalysts are titrated with CS2 the decrease in rate is linear unless mass transfer limitations occur. 

Boitiaux, J.P., Cosyns, J. and Verna, F. (1987) Poisoning of hydrogenation catalysts. How to cope with this general problem Stud. Surf. Sci. Catal., 34, 105. 

As an example of low-temperature catalytic reactions, hydrogenation of unsaturated hydrocarbons is the most important industrial application. Chemical industrial needs are mainly for unsaturated hydrocarbons, which have reactivities that enable polymer or petrochemical product development. All the processes developed for the production of olefins, diolefins, and aromatics give a mixture of unsaturated hydrocarbons, which are not valuable as such further hydrogenations are necessary to obtain usable products for refining and chemical industry. Sulfur is generally considered to be a poison of hydrogenation catalysts. But in the case of hydrodehydrogenation reactions, this compound can also be used as a modifier of selectivity or even, in some cases, as an activator. 

Sulfur is generally considered to be a poison of hydrogenation reactions. However, in commercial hydrogenation and dehydrogenation reactions, sulfur is also used as a modifier, and in some cases as activator of catalytic hydrogenation reactions. Barbier and co-authors review the Role of Sulfur in Catalytic Hydrogenation Reactions. ... 

Inhibition of chemi-desorption reactions is probably mainly caused by the CO, which is known to be strongly adsorbed on the Fischer Tropsch catalyst metals and which is also known as a poison of hydrogenation reactions or a firmly bound tt-1 igand in coordination chemistry, which reacts via insertion. Thus in this paper a kinetic concept of Fischer Tropsch surface polymerization is developed, whereas the nature of surface species is only regarded in general. 

One method of combating poisoning of hydrogen electrodes by CO is to modify the catalyst using an approach in which the relative strength of the chemisorbed CO bond is reduced. It is more than 30 years since the discovery of Pt/Ru as an electrocatalyst which is relatively tolerant of CO (relative to pure Pt), and no significantly better electrocatal5dic system has yet been foimd. 

Camara GA, Ticianelli EA, Mukerjee S, Lee SJ, McBreen J (June 2002) CO poisoning of hydrogen oxidation reaction in PEMECs. J Electrochem Soc 149(6) A748-753... 

Although there are alternative theories, the global reaction mechanism of CO poisoning of hydrogen PEFCs with platinum catalyst has been modeled by Springer and co-workers [79] ... 

This reaction is an undesirable side reaction in the manufacture of hydrogen but utilised as a means of removing traces of carbon monoxide left at the end of the second stage reaction. The gases are passed over a nickel catalyst at 450 K when traces of carbon monoxide form methane. (Methane does not poison the catalyst in the Haber process -carbon monoxide Joes.)... 

Mandelic acid. This preparation is an example of the synthesis of an a-hydroxy acid by the cyanohydrin method. To avoid the use of the very volatile and extremely poisonous hquid hydrogen cyanide, the cyanohydrin (mandelonitrile) is prepared by treatment of the so um bisulphite addition compound of benzaldehj de (not isolated) with sodium cyanide ... 

Conditions of hydrogenation also determine the composition of the product. The rate of reaction is increased by increases in temperature, pressure, agitation, and catalyst concentration. Selectivity is increased by increasing temperature and negatively affected by increases in pressure, agitation, and catalyst. Double-bond isomerization is enhanced by a temperature increase but decreased with increasing pressure, agitation, and catalyst. Trans isomers may also be favored by use of reused (deactivated) catalyst or sulfur-poisoned catalyst. 

Phosphoric Acid Fuel Cell. Concentrated phosphoric acid is used for the electrolyte ia PAFC, which operates at 150 to 220°C. At lower temperatures, phosphoric acid is a poor ionic conductor (see Phosphoric acid and the phosphates), and CO poisoning of the Pt electrocatalyst ia the anode becomes more severe when steam-reformed hydrocarbons (qv) are used as the hydrogen-rich fuel. The relative stabiUty of concentrated phosphoric acid is high compared to other common inorganic acids consequentiy, the PAFC is capable of operating at elevated temperatures. In addition, the use of concentrated (- 100%) acid minimizes the water-vapor pressure so water management ia the cell is not difficult. The porous matrix used to retain the acid is usually sihcon carbide SiC, and the electrocatalyst ia both the anode and cathode is mainly Pt. 

The methanation reaction is currently used to remove the last traces (<1%) of carbon monoxide and carbon dioxide from hydrogen to prevent poisoning of catalysts employed for subsequent hydrogenation reactions. Processes for conversion of synthesis gas containing large quantities of carbon monoxide (up to 25%) into synthetic natural gas have been investigated to serve plants based on coal-suppHed synthesis gas. 

Cyanohydrins are highly toxic by inhalation or ingestion, and moderately toxic through skin absorption (21). AH a-hydroxy nitriles are potential sources of hydrogen cyanide or cyanides and must be handled with considerable caution. Contact with the skin and inhalation should be rigorously avoided. Special protective clothing should be worn and any exposure should be avoided (18,20). The area should be adequately ventilated. Immediate medical attention is essential in case of cyanohydrin poisoning. 

The catalyst sometimes loses its activity when about half of the theoretical amount of hydrogen has been absorbed, probably because of the poisoning action of impurities not removed from the commercial cholesterol. In such a case the addition of one or two 0.2-g. portions of catalyst usually sufiices to bring the reaction practically to completion. 

The influence of Zn-deposition on Cu(lll) surfaces on methanol synthesis by hydrogenation of CO2 shows that Zn creates sites stabilizing the formate intermediate and thus promotes the hydrogenation process [2.44]. Further publications deal with methane oxidation by various layered rock-salt-type oxides [2.45], poisoning of vana-dia in VOx/Ti02 by K2O, leading to lower reduction capability of the vanadia, because of the formation of [2.46], and interaction of SO2 with Cu, CU2O, and CuO to show the temperature-dependence of SO2 absorption or sulfide formation [2.47]. 

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