关键词: Biomass, NO_x reduction, Activated carbon, Selectivity

Abstract: In this study, to prepare a series of activated carbon-supported metals for the catalytic reduction of NO_x to N₂ in excess O₂, activated carbons derived from lignocellulosic and herbaceous biomasses were selected as the reducing agents, and alkali and transition metals were used as the catalytic active phases. The effects of the type of biomass, carbonization temperature and catalyst composition on NO_x reduction efficiency were analyzed in a fixed-bed flow reactor. The results showed that two temperature regimes are present for the NO_x-carbon reaction:at temperatures below 250℃, the NO_x adsorption process on the carbon surface was predominant, whereas true NO_x reduction by carbon occurred at temperatures above 250℃, producing N₂, CO₂ and CO. The influence of the carbonization temperature on carbon reactivity depended on the effect of the carbonization temperature on the carbon surface area and the reduction of the metal species on carbon. All studied metals catalyzed both NO_x and O₂ reduction by carbon, and potassium could strongly enhance the C-NO_x reaction without substantial carbon consumption by O₂. Moreover, the potassium supported by sawdust-derived activated carbon exhibited higher selectivity and capacity towards NO_x reduction than did its previously reported coal-derived counterparts. These properties were ascribed to the high dispersion of the active potassium species on the carbon surface, as observed through the comparison of X-ray photoelectron spectroscopy and powder X-ray diffraction results for the carbons made from biomass and coal-based precursors.

Key words: Biomass, NO_x reduction, Activated carbon, Selectivity