NO oxidation over activated carbon fiber (ACF). Part 1. Extended kinetics over a pitch based ACF of very large surface area

Kinetics on the oxidation of NO was studied over a pitch based activated ca rbon fiber of very large surface area (pitch ACF) by changing NO and O-2 co ncentrations in a flow reactor. NO was initially removed through adsorption until saturation, increasing gradually its outlet concentration. In the me an time, NO2 was found in the gas phase after an induction period to increa se its concentration very early to the stationary one. It is noted that a m aximum NO concentration was observed just before reaching the stationary co ncentration, where the adsorption of NO was almost saturated. High concentr ations of both O-2 and NO increased the amount of saturated adsorption and the stationary conversion of NO, Freundlich equation being well fitted to t he observed adsorption and conversion. The reaction order larger than unity in NO suggests multi-molecular intermediate over the ACF surface for oxida tion as the dimer has been proposed in the gas phase oxidation of NO. The m ajor adsorbed species found was NO2 over the ACF surface in the stationary state, although some NO was also found in TPD profile of adsorbed species e ven in the stationary state. Some reduction of surface NO2 at its desorptio n is suggested. A peculiar peak of the maximum NO concentration observed be fore the stationary conversion may reflect participation of NO to the multi -molecular intermediate which requires a large coverage of adsorbed NO2 bef ore rapidly releasing NO2 from the surface to the gas phase. (C) 2000 Publi shed by Elsevier Science Ltd.