Elimination reactions, bond-order increase

Hydrocarbons (HCs) from C2 to CIO are commonly used to test activity. The efficiency of the HC in the SCR of NOx in competition with the combustion reaction with oxygen increases with increasing molecular weight. This is probably due to the parallel increase in the heat of adsorption and decrease in the C-H bond strength.132 Alkanes, alkenes and oxygenated HCs have been studied in this reaction and the activity in the NOx elimination frequently follows this order, with the lower light-off temperatures being displayed for the latter type of compounds. Independent of the nature of... 

E2 reactions are favoured over SN2 reactions by using high temperatures. In general, increasing the reaction temperature leads to more elimination. This is because the elimination reaction has a higher activation energy (than the substitution reaction), as more bonds need to be broken in order to form the alkene product. 

In an elimination reaction, atoms or groups that are bonded to adjacent atoms are eliminated as a small molecule. Typically, the order of the bond between the two adjacent atoms increases as a result of the elimination, as shown in the example below ... 

The per cent of dicyclohexylamine formed in hydrogenation of aniline increases with catalyst in the order ruthenium < rhodium platinum, an order anticipated from the relative tendency of these metals to promote double bond migration and hydrogenolysis (30). Small amounts of alkali in unsupported rhodium and ruthenium catalysts completely eliminate coupling reactions, presumably through inhibition of hydrogenolysis and/or isomerization. Alkali was without effect on ruthenium or rhodium catalysts supported on carbon, possibly because the alkali is adsorbed on carbon rather than metal (22). 

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