Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Poisoning of hydrogenation catalysts

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. [Pg.75]

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. [Pg.280]

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 ... [Pg.25]

Steam. Steam is a potential poison of nickel catalysts under extremely high steam concentrations and low hydrogen concentrations. This is apparent in Figure 11 where the equilibrium ratio of Ph2/Fh2o over Ni and over Ni(active) is plotted as a function of temperature for the following reactions ... [Pg.27]

Electro-catalysts which have various metal contents have been applied to the polymer electrolyte membrane fuel cell(PEMFC). For the PEMFCs, Pt based noble metals have been widely used. In case the pure hydrogen is supplied as anode fuel, the platinum only electrocatalysts show the best activity in PEMFC. But the severe activity degradation can occur even by ppm level CO containing fuels, i.e. hydrocarbon reformates[l-3]. To enhance the resistivity to the CO poison of electro-catalysts, various kinds of alloy catalysts have been suggested. Among them, Pt-Ru alloy catalyst has been considered one of the best catalyst in the aspect of CO tolerance[l-3]. [Pg.637]

The strategy of introducing water as second phase has been used by Greenfield for obtaining higher yields of dibenzylamine (>97%) by hydrogenation of benzonitrile. In this case, water seems to prevent poisoning of the catalyst (Doraiswamy and Sharma, 1984). [Pg.141]

Davis 69) found no considerable variation in the o-xylene versus ethylbenzene ratio as a function of hydrogen pressure. He also observed that the relative amount of o-xylene from n-octane increased (a) with decreasing Pt loading of the catalyst (70) b) with increasing tin addition 69, 7J) (c) with the poisoning of the catalyst with thiophene (77) and d) if octenes or octynes... [Pg.289]

The presence of benzo[6]thiophene in commercial naphthalene, its possible contamination with isomeric thienothiophenes 1 and 2, and their ability to poison aromatic hydrogenation catalysts led Maxted and Walker to develop detoxification by a preliminary short hydrogenation, in which thienothiophenes 1 and 2, and benzo[6]-thiophene are adsorbed on the catalyst. This is followed by their hydrogenation products that can easUy be oxidized with hydrogen peroxide or permolybdic acid to nontoxic sulfones subsequent hydrogenation of the aromatic hydrocarbons is then performed as usual. [Pg.180]

If the exchange of any hydrocarbon obeys Equation (5), one can deduce that all the hydrogen atoms in the molecule are equally susceptible to exchange. Consequently, failure to obey this equation may provide a useful indication of differences in reactivity between the various types of hydrogen atoms in the hydrocarbon, but this must be confirmed by devising and testing new equations because poisoning of the catalyst may also lead to failure of the equation. [Pg.230]

The poisoning of a catalyst may be shown by adding some hydrogen sulfide solution to the hydrogen peroxide before the colloidal platinum is introduced. No decomposition of the peroxide is observed in this case, since the platinum has been poisoned by the presence of the hydrogen sulfide. This method is applicable to most of the metals below hydrogen in the electrochemical series. [Pg.164]

Methanation, that is, the transformation of CO to methane222 270-272 [Eq. (3.1), reverse process], was developed in the 1950s as a purification method in ammonia synthesis. To prevent poisoning of the catalyst, even low levels of residual CO must be removed from hydrogen. This is done by methanation combined with the water-gas shift reaction.214,273,274 In the 1970s the oil crises spurred research efforts to develop methods for substitute natural-gas production from petroleum or coal via the methanation of synthesis gas. ... [Pg.108]

A major problem in noble metal catalyzed liquid phase alcohol oxidations -which is principally an oxidative dehydrogenation- is poisoning of the catalyst by oxygen. The catalytic oxidation requires a proper mutual tuning of oxidation of the substrate, oxygen chemisorption and water formation and desorption. When the overall rate of dehydrogenation of the substrate is lower than the rate of oxidation of adsorbed hydrogen, noble metal surface oxidation and catalyst deactivation occurs. [Pg.385]

The character of the chemisorption of nitrogen can be also judged from the results of studies of ammonia synthesis kinetics at the reversible poisoning of the catalyst with water vapor (102,103). If a gas mixture contains water vapor, an adsorption-chemical equilibrium of adsorbed oxygen, hydrogen gas, and water vapor sets in on the iron catalyst. [Pg.261]

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. [Pg.867]

These experiments show that coronene can be hydrogenated in the same temperature range as, e.g., naphthalene, but splitting is by far slower. It seems, however, that this is due not to higher stability of the coronene itself, but rather to a poisoning of the catalyst activity. It can be speculated that at hydrogen pressures above 800 atm., pressures which would prevent condensation reactions, coronene could be split easily. Support for this assumption is the observation that the presence of coronene decreases the splitting activity of the WS2 catalyst toward other... [Pg.257]

The addition of 0.5 to 10 percent by volume of H2 to the natural gas feed has been shown to keep the nickel in the reduced state, which makes it more active. Also, the hydrogen will retard the formation of nickel sulfide, which will prevent or minimize poisoning of the catalyst ... [Pg.68]


See other pages where Poisoning of hydrogenation catalysts is mentioned: [Pg.225]    [Pg.56]    [Pg.40]    [Pg.43]    [Pg.303]    [Pg.225]    [Pg.56]    [Pg.40]    [Pg.43]    [Pg.303]    [Pg.118]    [Pg.1541]    [Pg.284]    [Pg.23]    [Pg.91]    [Pg.306]    [Pg.151]    [Pg.50]    [Pg.361]    [Pg.484]    [Pg.72]    [Pg.73]    [Pg.20]    [Pg.284]    [Pg.327]    [Pg.356]    [Pg.365]    [Pg.73]    [Pg.152]    [Pg.233]    [Pg.881]    [Pg.163]    [Pg.354]    [Pg.259]    [Pg.602]    [Pg.211]   
See also in sourсe #XX -- [ Pg.4 , Pg.8 , Pg.17 ]




SEARCH



Catalyst poison

Catalysts catalyst poisoning

Catalysts poisoning

Hydrogenation of catalysts

Hydrogenation poisoning

Poisoned catalysts

Poisoning of hydrogenation

Poisoning, of catalysts

Poisons of catalyst

© 2024 chempedia.info