Understanding of Soot Removal Mechanism over DeNOx‑Catalysts as Passive Converters

• Published in: Industrial & engineering chemistry research 2021-05, Vol.60 (18), p.6501-6511
• Main Authors: Cortés-Reyes, Marina, Herrera, Concepción, Larrubia, M. Ángeles, Alemany, Luis J
• Format: Article
• Language: English
• Subjects: Kinetics, Catalysis, and Reaction Engineering
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/acs.iecr.0c05363

Although diesel particulate filters (DPFs) are able to efficiently remove soot and coupled NO x storage and reduction and selective catalytic reaction (NSR–SCR) technologies can considerably decrease NO x emissions, the elimination of soot over Pt–Ba–K/Al2O3 and Cu-CHA NO x removal catalysts acting as passive converters is still an open topic. The estimation of the occurrence frequency and activation energy values from the distribution function of activation energy allowed the identification of sequential steps involved in the soot removal. For that, TG-MS nonisothermal experiments were carried out over the model of deNO x catalysts under a NO+O2 atmosphere. For bare soot, only gas-phase components react with carbon particles to produce CO2 at high temperatures with E a values higher than 120 kJ mol–1 for the direct oxidation by molecular oxygen and 114 kJ mol–1 for the assisted soot removal process by NO x . For the lean NO x trap (LNT) model catalyst, the combination of hydroxylated centers, provided by the incorporation of potassium responsible for the carbon elimination via gasification (70–90 kJ mol–1), and nitrate species stored onto the surface, involved in the elimination via oxidation (97 kJ mol–1), together with the gas-phase interaction, makes this catalyst an efficient soot passive converter. The Cu-SAPO-34 SCR catalyst with 4 wt % of copper located inside the framework and small pores of the chabazite structure are not able to act as a converter because soot removal takes place via assisted combustion with NO x and molecular oxygen, similar to the uncatalyzed process. CeO2, the main component of DPF, presented the lowest values of T 90 (923 K), ignition soot temperature, and activation energy due to the intervention of highly reactive oxygen species being the most effective soot converter in the low-temperature range.