The effect of low-concentration SO2 on the adsorption of NO over activ
ated carbon was studied using adsorption-desorption profiles obtained
during thermal analysis-mass spectrometry. Using three different gas m
ixtures and adsorption temperatures between 293 and 413 K with NO and
SO2 as the reactants, it was determined that NO2 and SO2 were the prim
ary adsorbed species. The uptake of NO2 decreased with increasing temp
erature, whereas the uptake of SO2 was independent of temperature. Exc
ept at the highest adsorption temperatures, the amount of NO2 adsorbed
was greater than that of SO2 adsorbed. The presence of SO2 inhibited
adsorption of NO2, but the co-adsorption of NO2 promoted the adsorptio
n of SO2. These data point to the possibility that the SO2 binding sit
es on the carbon are associated with the reaction NO + 1/2O(2) --> NO2
, and to the different adsorption mechanisms which control NO2 and SO2
uptake. (C) 1997 Elsevier Science Ltd.