Investigation of the activity of unburned carbon as a catalyst in the decomposition of NO and NH3

The paper presents the assessment of the suitability of unburned carbon from lignite fly ash for the reduction of NO from boiler flue gas in the presence of NH3 as a reducing agent. The catalytic properties were characterized based on: identification and quantification of surface oxygen functional groups (TGA-FTIR-DSC), identification and evaluation of the strength of active sites (TPD-NH3/CO2), determination of bed porosity and laboratory tests in a fixed bed reactor. The conditions in an industrial boiler have been proved to favour the formation of acidic and neutral groups, as well as acid and basic active sites of a wide strength range. Based on the results obtained, plausible mechanisms on unburned carbon have been proposed, i.e. the reduction of NO is controlled by two successive stages: with the participation of C-OH and C=O groups. It has been shown that NH3 chemisorption is the resultant of the presence of strong acid sites and bed porosity. The research results presented in the paper show that unburned carbon has surface properties that are competitive with the active carbons available on the market, both in the context of reducing NO emissions and reducing the effect of ammonia slip.