Characteristics of NO_x adsorption and surface chemistry on impregnated activated carbon

Abstract

Adsorption characteristics of NO _x 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 NO _x 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 NO _x 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 NO _x . 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 NO _x was improved.

Keywords:

• NO _x
• KOH
• Impregnated activated carbon
• Time of flight secondary ion mass spectrometry
• Adsorption
• Surface chemistry

Acknowledgments

We are grateful to Dr. Yeon-Hee Lee of the Korea Institute of Science and Technology for her valuable discussion and experimental help with ToF-SIMS and SIMS depth profiles.