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

• Published in: Fuel (Guildford) 2022-02, Vol.309, p.122170, Article 122170
• Main Authors: Kisiela-Czajka, Anna M., Hull, Sylwia, Albiniak, Andrzej
• Format: Article
• Language: English
• Subjects: Ammonia; Ammonia slip; Boilers; Carbon; Carbon dioxide; Catalysts; Chemisorption; Emissions; Fixed bed reactors; Fixed beds; Flue gas; Fly ash; Functional groups; Laboratory tests; Lignite; NH3; Oxygen surface functional groups; Porosity; Reducing agents; Surface properties; Unburned carbon
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2021.122170

[Display omitted] •The reduction of NO is controlled by two stages;•NH3 reacts with the phenolic hydroxyl group, NO reacts with the carbonyl group;•NH3 conversion is the resultant of the availability index of strong acid active sites;•The successful use of TGA for the needs of TPD-CO2;•The successful use of TGA-FTIR-DSC for the analysis of surface oxygen functional groups; 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.