THE SELECTIVE REDUCTION OF SO3 TO SO2 AND THE OXIDATION OF NO TO NO2 BY METHANOL

The article reports the discovery of a new homogeneous gas phase reaction in which methanol converts SO3 to SO2. In the course of this reaction NO is converted to NO2. This new reaction is highly selective in that ppm concentrations of SO3 and NO are converted by equivalent quantities of methanol, even in the presence of large excesses of O2. Both the conversion of SO3 to SO2 and NO to NO2 are reversible in that at any given temperature there is an optimal reaction time; the use of longer reaction times causes decreasing conversion. For the optimal temperature the reaction is also rapid, capable of achieving better than 80% reduction in only 55 ms. The existence of this new reaction was predicted by computer modeling. Subsequent experiments verified the predicted modeling trends. The mechanism by which methanol simultaneously reduces SO3 and oxidizes NO involves methanol functioning as a source of HO2 free radicals, which then initiate the reactions NO + HO2 = NO2 + OH, SO3 + HO2 = HSO3 + O2, and HSO3 + M = SO2 + OH. © 1990.