Low temperature catalytic oxidation of NO over sludge char under different pyrolysis activation conditions

Catalytic oxidation of NO (CONO) at ambient temperature over sludge char (SC) prepared from sewage sludge was studied in this paper. The influencing mechanism of sludge pyrolysis/activation parameters on the CONO were investigated for the SC prepared with different pyrolysis temperatures (600, 700, and 800 ℃) and different mass ratios of dried sludge (DS) to KOH (DS/KOH = 4∶1, 3∶1, 2∶1, and 1∶1). The results indicated that both pyrolysis temperature and KOH activation had great influence on the catalytic performance of SC. With the increase of temperature from 600 to 800 ℃, the NO conversion increased from 12% to 36%. However, the catalytic activity of KOH-activated SC increased and then decreased with the increase of KOH content. The SC prepared under the pyrolysis temperature of 700 ℃ and the DS/KOH mass ratio of 3∶1 showed the best catalytic performance with NO conversion of 56%. The NO conversion further increased to 76.5% when the SC was reduced by H₂. It was also found that there was a strong correlation between the catalytic activity and the specific surface area of the SCs. The reaction might follow the Eley-Rideal (E-R) mechanism.