| OCR Text |
Show higher H02 and lower H concentrations, the effective rate of NO oxidation is increased since, as shown above, H02 radicals convert NO to N02 and H atoms reduce N02 to NO. At 1000 K which is higher than the optimum temperature, methanol removes NO to a level of about 40 ppm and then NO is partially reconverted to N02 through a homogeneous reaction mechanism This homogeneous reconversion process involves an increase in concentrations of H atoms at relatively high temperatures followed by their reaction with N02 (69). The kinetic modeling also predicted some homogeneous N02-to-NO reconversion in the high temperature region of H20 2 injection, but with much lower efficiency than for CH30H injection. Slow reconversion at lower temperatures, as indicated in the experiments, was not noticed by the modeling and is most likely explained by heterogeneous processes which were not included in the mechanism. The efficiency of the H20/CH30H mixture in NO removal was found to be higher than that of each component individually. This is explained by the more easy formation of OH radicals from H20 2• The hydroxyl radicals formed can initiate chain reactions with both H20 2 and CH30H. Thus, the presence of H20 2 in mixtures with CH30H promotes the efficiency of NO removal. Hydrogen peroxide also shifts the temperature window for NO control to lower temperatures while decreasing the amount of CO fonned from CH30H. The use of mixtures of H20 2-CH30H with various compositions can make the rrethod of NO removal flexible because one can add as much CH30H as possible within CO regulatory limits, and then add enough H20 2 to obtain target NO conversion. ExperiIrental data demonstrated that the performance of NO removal by injection of hydrogen peroxide is relatively independent of initial oxygen concentration. On the other hand, as shown above, the reaction of NO with methanol needs oxygen for oxidation of the CH20H radicals (63). Modeling qualitatively explains these features of NO reactions, however, modeling does not show 15 . |
