Abstract
The reactivity of various hydrocarbons and light oil was investigated for the selective catalytic reduction of NOx in diesel engine exhaust over Co-Al2O3 and Co-mordenite. The order of reactivity of hydrocarbon species over Co-Al2O3 was the same as that over Co-mordenite, when molecular weights of hydrocarbons were almost equal. That order was n-paraffins>isoparaffins>aromatics. The contributions of n-paraffins in NOx conversion above 500°C were controlled by the amount of carbon atoms added, not by that of n-paraffins molecules, except for methane and ethane. The reactivity of hydrocarbons for NOx reduction was correlated with the combustibility of hydrocarbons.
Although the am ount of total hydrocarbon added increased, the NOx conversion decreased by addition of aromatics to n-dodecane. The NOx reduction, therefore, was retarded by addition of aromatics. The retarding effect of aromatics on NOx reduction increased with increased molar amount of aromatics added over Co-Al2O3. The ratio of decrease of NOx conversion by addition of toluene to n-dodecane was the same as that in case of addition of 1-methyl-naphthalene. The retarding effect of toluene over Co-mordenite also increased with increasing the molar amount of toluene added. On the other hand, when n-dodecane was mixed with 1-methyl-naphthalene, the NOx conversion was constant regardless of molar amount of 1-methyl-naphthalene added. Light oil, extracted of aromatics, showed reactivity higher than that of the original light oil over Co-Al2O3 and Co-mordenite.
