Hydrogen poisoning action

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. 

To prevent the poisoning action of hydrogen peroxide and catalyst life increase [51], the reaction system and the catalyst are added to by substances, i.e. stabilizers of the catalyst operation. They were ionol, hydroquinone, diphenyl amine and diphenylguanidine. 

The poisoning action of the heavy metals is in accord with their known tendencies to decompose hydrocarbons, at cracking temperatures, to carbon and hydrogen. The mechanism of poisoning is believed not to consist of inactivation of the active centers of the catalyst, but rather a superimposition of heavy-metal-type cracking upon the normal cracking... 

The importance of the details of pretreatment of chromia catalysts has often not been recognized nor, in some of the earlier work, the strong poisoning action of water vapor. Thus, the temperatures listed in Table I may be higher than necessary under optimum conditions. For example, one would conclude from Lazier and Vaughen (2) and Frey and Huppke (3), that the hydrogenation of olefins on chromia would require temperatures of about 300°. However, Weller and Voltz (8) discovered that the hydrogenation of ethylene could be effected at — 78° on well-activated chromia under anhydrous conditions. 

The preferential oxidation process consists of adding sufficient air to the mixed gas to give a slight excess over that required for the oxidation of the monoxide, saturating the mixture with water vapor at a temperature somewhat above room (about 40° C.) and passing it over the catalyst contained in narrow bore copper tubes immersed in a temperature controlled liquid bath. The water vapor exhibits a selective poisoning action toward hydrogen oxidation, 5 apparently independent of concentration and of catalyst temperature. 

Hydrogen sulfide is the only thermodynamically stable sulfane it occurs widely in nature as a result of volcanic or bacterial action and is, indeed, a prime source of elemental 8 (p. 647). It has been known since earliest times and its classical chemistry has been extensively studied since the seventeenth century.H28 is a foul smelling, very poisonous gas familiar to all students of chemistry. Its smell is noticeable at 0.02 ppm but the gas tends to anaesthetize the olefactory senses and the intensity of the smell is therefore a dangerously unreliable guide to its concentration. H28 causes irritation at 5 ppm, headaches and nausea at 10 ppm and immediate paralysis and death at 100 ppm it is therefore as toxic and as dangerous as HCN. 

Sulfur. It is not readily predictable from existing thermodynamic data that sulfur would be a poison of nickel catalysts. The action of sulfur is undoubtedly through the reaction of hydrogen sulfide with nickel, according to ... 

Kretzschmar R, Meyer HJ, Teschendorf HJ, Zollner B (1969). [Antagonistic action of natural 5,6-hydrogenated kava pyrones against strychnine poisoning and experimental local tetanus]. Arch Int Pharmacodyn Ther. Dec. 182(2) 251-68. 

Health and Safety Factors. Carbonyl sulfide is dangerously poisonous, more so because it is practically ododess when pure. It is lethal to rats at 2900 ppm. Studies show an LD5Q (rat, ip) of 22.5 mg/kg. The mechanism of toxic action appears to involve breakdown to hydrogen sulfide (36). It acts principally on the central nervous system with death resulting mainly from respiratory paralysis. Litde is known regarding the health effects of subacute or chronic exposure to carbonyl sulfide a 400- Jg/m3 max level has been suggested until more data are available (37). Carbon oxysulfide has a reported inhalation toxicity in mice LD5Q (mouse) = 2900 ppm (37). 

C2 HjN2 Oj-NH, obtained by the action of ain- monia on nitromethane, dec on heating with evoln of poisonous hydrogen cyanidefRef 3). 

Antidotes.—Two classes of agents axe known, which lessen or destroy the poisonous effects of lead thess are sulphide of hydrogen and the soluble metallic sulphides, snd sulphuric aeid and the soluble sulphates. With the first class, black sulphide of lead is immediately formed, and as this body is almost inert, if not imm cuoue, the further deleterious action of the lead salt is... 

---