Characteristics of NOx adsorption and surface chemistry on impregnated activated carbon

Adsorption characteristics of NOx were studied with granular activated carbon (GAC) impregnated with potassium hydroxide (KOH). To confirm the selective adsorptivity of KOH- impregnated activated carbon (K-IAC) to NOx in a fixed-bed adsorption column, temperature of 303-403K, linear velocity of 10-32 cm/sec, and effect of added oxygen were observed. Using scanning electron microscopy (SEM), time of flight secondary ion mass spectrometry (ToF-SIMS), and SIMS depth profile, surface-reaction phenomena of adsorbent, caused by the KOH impregnation and NOx adsorption, were investigated. NO2 adsorbs by chemical reaction with impregnated KOH, from which NO is generated. When oxygen exists, the NO again adsorbs to NO2 with oxygen chemisorbed on the surface, which increases the adsorptivity. In the results of ToF-SIMS and SIMS depth profile, NO2- and NO3- increased at the surface distribution by forming oxide crystals of KNO2 and KNO3 due to bond formation with potassium ions. The SIMS depth profile of KO- ensured that KOH provided the selective adsorption site of NOx. In the mechanism studied, the basic character was led on K-IAC by surface basic OH- ions of KOH, oxidation rate from KNO2 to KNO3 was delayed, and adsorptivity of K-IAC to NOx was improved.