Inhibition by hydrogen

The presence of alkali and alkaline earth chlorides may also hinder precipitation of the sulphide thus, from a 0001 molar solution of lead chloride in water at 20° C., precipitation is completely inhibited by hydrogen chloride alone if in a concentration of 1-riV, and by decreasing concentrations of the acid in the presence of increasing quantities of calcium, ammonium or potassium chloride. Cadmium sulphide, precipitated from hydrochloric acid solution, contains adsorbed chlorine,1 the amount depending on the conditions of the precipitation the precipitation is incomplete at 80° C. 

The inhibition by hydrogen was obviously more pronounced in the micro channels. Without hydrogen in the feed, the reaction rate was on average 34% higher for the coated catalysts. The kinetic expression described the reaction rate experimentally observed with an error of < 15% for the packed bed and < 20% for the micro channels (see Figure 2.6) [24]. 

Nicell JA, Wright H. A model of peroxidase activity with inhibition by hydrogen peroxide. Enzyme Microb Technol 1997 21 302-310. 

Bonn6 [1] studied reaction kinetics of tetraphenylporphyrin model compounds over several catalysts and concluded that hydrogenation and hydrogenolysis occur on different sites. Therefore the reaction mechanism of VO-TPP hydrodemetallisation is described by a two-site model. It was also found that a Langmuir-Hinshelwood type of kinetics applies with small inhibition by hydrogen. 

This does not immediately suggest a mechanism or the location of the active centres, but the strong inhibition by hydrogen might indicate its slow reversible release from a water molecule or from hydroxyl groups that it has formed (see Scheme 10.1). This cycle can of course work in either direction. 

Ruthenium and rhodium are more susceptible to inhibition by hydrogen halides than are platinum and palladium. Under mild conditions ruthenium is inhibited even by acetic acid, which is generally a good solvent for hydrogenations over rhodium, palladium, and platinum. Hydrogen chloride may become an inhibitor for rhodium-catalyzed hydrogenations. Freifelder has shown that hydrochloric acid is a strong in-... 

Eisenberg and Bliss and Palmer et al have studied the time-course of the methane pyrolysis there is an initial acceleration followed by retardation. Both studies show that ethane accelerates the reaction. The work of Palmer et indicates that there is a deposition of vitreous carbon on the walls of the vessel, that the reaction is inhibited by carbon, and that the rate is not appreciably affected by the surface volume ratio. They also find that the reaction is strongly accelerated by added naphthalene, which tends to produce carbon nuclei very rapidly. They conclude that the formation of nuclei has a strong effect on the rate of decomposition. The inhibition by hydrogen may then be due to its removal of nuclei. The accelerating effect of added ethane is attributed to its more rapid decomposition, with accompanying formation of nuclei aside from this, ethane is a good source of free radicals. 

Leglise, J. Van Gestel, J. Duchet, J.C. Promotion and inhibition by hydrogen sulfide of thiophene hydrodesulfurisation over a sulfide catalyst. 

Analysis of this rate equation shows that it takes into consideration the reversible reaction step in the steam reforming. The rate equation implies that the forward reaction is first order with respect to methane, zero order with respect to steam (possibly due to the high steam /C ratio in the experiments) and is inhibited by hydrogen. The reverse reaction is independent of the methane concentration, second order in hydrogen, first order in CO and is inhibited by H2O. 

It was also found that inhibition of both T-lymphocytes and T-helper cells by penicillamine and Cu(II)sulphate or ceruloplasmin could not be blocked by Cu-Zn SOD but was completely blocked by catalase, suggesting mediation of inhibition by hydrogen peroxide [655]. Mononuclear phagocytes, which were not inhibited by the combination of penicillamine and Cu(II)sulphate, were found to protect T-lymphocytes from this mixture as well as hydrogen peroxide, and the protective factor was found to be a soluble fraction of human monocyte or erythrocyte lysates. 

Figure I Butene dehydrogenation. Partial pressure and coke profiles inside a catalyst particle. Parallel-consecutive coking mechanism and inhibition by hydrogen.

The empirical equation expressing the experimental results shows that the reaction is inhibited by hydrogen bromide, but in a way which becomes relatively less serious the higher the concentration of bromine. Evidently hydrogen bromide and bromine are in competition for something which is necessary for the continuation of the chain, the only probable competitor to reaction (3) being... 

The inhibition by hydrogen was obviously more pronounced in the microchannels. Without hydrogen in the feed, the reaction rate was on average 34% higher for... 

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