Effect of Pressure on NO x Adsorption by Activated Carbons

Exposing activated carbons to nitric oxide and oxygen at temperatures between 295 and 400 K leads to the conversion of the NO to NO 2 at the carbon surface and the adsorption of NO 2 . In the current study, the conversion and adsorption kinetics of the NO to NO 2 reaction were examined at total pressures between 1 and 28 bar using a commercially available activated carbon. Up to 144 mg of NO 2 /g of carbon was adsorbed at 28 bar and 343 K, of which 115 mg of NO 2 /g of carbon was reversibly adsorbed−desorbed during repeated pressurization−depressurization cycles. The amount of NO 2 adsorbed at 17 bar and 373 K was similar to the amount adsorbed at 1 bar and 343 K, whereas it was 3−4 times greater than the amount adsorbed at 1 bar and 373 K. Analysis of the adsorption isotherm suggested the mechanism of NO 2 uptake was associated with micropore filling with a monolayer of adsorbed NO 2 formed at a total gas pressure near 10 bar. Time profiles for the desorption of NO 2, CO 2, and O 2 during pressure release and temperature-induced desorption suggested the influence of critical temperatures and pressures of the adsorbed gases and that van der Waals adsorption forces are important during adsorption and condensation within the pores of the carbon.