Hydrocarbons relative hydrogenation rates

J. Relative Hydrogenation Rates of Carbon Monoxide, Hydrocarbons, and Oxygenates... 

The relative rates of reaction of ethane toluene and ethylbenzene with bromine atoms have been measured The most reactive hydrocarbon undergoes hydrogen atom abstraction a million times faster than does the least reactive one Arrange these hydrocarbons in order of decreasing reactivity... 

Fig. 10. (a) Relative hydrogenation reactivities of selected aromatic hydrocarbons (CoMoS /Al203, 7.5 MPa, 325°C). Normalized rate constants are shown above the arrows, and equilibrium concentrations at the specified conditions are shown below the compounds (5). (b, facing page) Relative hydrogenation reactivities of selected aromatic hydrocarbons (CoMoS /Al203,69 MPa, 427°C). Rate constants are shown above the arrows, and equilibrium concentrations at 69 and 3.1 MPa are shown below the compounds (35). 

Goy et have studied the reaction of CN radicals with hydrocarbons and hydrogen the CN radicals being produced by photolysis of ICN at 2537 A. Relative rate coefficients for H abstraction were obtained as a function of temperature for only C2H6-CH4 mixtures. For systems containing ethane-propane and propane alone no temperature dependence of the rate coefficient ratios were observed. For... 

From results obtained with metallic and metallic oxide catalysts they conclude, that metallic catalysts do not accelerate the oxidation of hydrogen and carbon monoxide so exclusively as do the metallic oxide catalysts. With a metal catalyst, all the gases present have to react with a temporary intermediate oxide. On the other hand, hydrogen and carbon monoxide can directly reduce the oxide catalysts even at low temperatures, while the hydrocarbons cannot. For this reason hydrogen and carbon monoxide are more readily formed with a metallic catalyst than with a metallic oxide catalyst. It is evident that they do not consider equilibrium relationships of any importance since the composition of products is explained on the basis of relative reaction rates. Although this attitude may be well taken on the basis of the results, the fact that methane is very unreactive and requires an active catalyst for oxidation at low temperatures to form intermediates does not seem to have been recognized. 

The relative basicities of aromatic hydrocarbons, as represented by the equilibrium constants for their protonation in mixtures of hydrogen fluoride and boron trifluoride, have been measured. The effects of substituents upon these basicities resemble their effects upon the rates of electrophilic substitutions a linear relationship exists between the logarithms of the relative basicities and the logarithms of the relative rate constants for various substitutions, such as chlorination and... 

Rate Constants k (mmole min g ) of Isolated Reactions, and Relative Reactivities S from Competitive Reactions Obtained in the Hydrogenation of Aromatic Hydrocarbons... 

Robertson et al.261 measured rates of bromination of some aromatic hydrocarbons in acetic acid containing sodium acetate (to eliminate protonation of the aromatic by liberated hydrogen bromide) and lithium bromide (to reduce the rate to a measurable velocity ) at 25 °C, the second-order rate coefficients for 3-nitro-N,N-dimethylaniline and anisole being 14.2 and 0.016 respectively the former compound was thus stated to be about 1012 times as reactive as benzene (though no measurement of the latter rate coefficient, inferred to be 1.33 xlO-11, could be found in the literature) and this large rate spread gives one further indication of the unreactive nature of the electrophile. Other rates relative to benzene were ... 

The influence of electronegative additives on the CO hydrogenation reaction corresponds mainly to a reduction in the overall catalyst activity.131 This is shown for example in Fig. 2.42 which compares the steady-state methanation activities of Ni, Co, Fe and Ru catalysts relative to their fresh, unpoisoned activities as a function of gas phase H2S concentration. The distribution of the reaction products is also affected, leading to an increase in the relative amount of higher unsaturated hydrocarbons at the expense of methane formation.6 Model kinetic studies of the effect of sulfur on the methanation reaction on Ni(lOO)132,135 and Ru(OOl)133,134 at near atmospheric pressure attribute this behavior to the inhibition effect of sulfur to the dissociative adsorption rate of hydrogen but also to the drastic decrease in the... 

---