Development of Novel Mn-based Catalysts for Low Temperature Selective Catalytic Reduction of Nitrogen Oxides with Ammonia
Nitrogen oxides (NOx) emitted from combustion processes in stationary installations and automobiles are regarded a major source of atmospheric contaminations, endangering human health by contributing to acid deposition, photochemical smog, and ozone depletion. Therefore, it is by legislation required to abate such emission to a very low level.
Selective catalytic reduction of NOx with ammonia (NH3) to make dinitrogen (N2) (i.e., NH3-SCR) is the most effective and most widely used technology to mitigate NOx emissions. Industrially applied NH3-SCR catalysts based on vanadium (VWT catalysts) exhibit high N2 selectivity and good thermal stability, but they require a relatively high operating temperature (300-400 °C). To avoid a costly reheating of the flue gas, it is thus necessary to locate the VWT catalyst upstream of dust removal and/or desulfurization units which lowers the flue gas temperature significantly. However, this position makes VWT catalysts prone to deactivation or inhibition by impurities in the flue gas such as SO2, alkali or heavy metals.
Manganese oxide (MnOx) catalysts exhibit much higher NH3-SCR activity at low-temperature (200 °C or lower) than VWT catalysts, and are thus attractive low cost and environmentally benign catalysts that can be utilized in a preferred “tail-end” SCR system without the need for flue gas reheating. Various strategies have previously been attempted for developing industrially viable MnOx catalysts, however, challenges such as too narrow temperature operating range, limited resistance to water, and susceptibility to SO2 poisoning have hampered their practical application.
This PhD thesis focuses on improving the applicability of MnOx catalysts for low-temperature NH3-SCR by developing strategies to expand the catalysts’ operational temperature window, improve N2 selectivity, and increase resistance to water and SO2. The pursued strategies include the rational constructing of novel manganese-titanium-cerium oxide core-shell catalysts, doping MnOx catalysts with metal like iron and aluminium, and optimizing the synthesis approaches of manganese-iron oxide catalysts. The work reported in the thesis provides significant progress in enhancing the performance of MnOx-based NH3-SCR catalysts and uncovers intriguing findings. This insight will inspire future catalyst design with enhanced applicability for removing NOx from industrial flue gases.
Principal Supervisor:
Professor Anders Riisager, DTU Chemistry
Co-supervisor:
Senior Researcher Leonhard Schill, DTU Chemistry
Professor Emeritus Rasmus Fehrmann, DTU Chemistry
Examiners:
Associate Professor Kaibo Zheng, DTU Chemistry
R&D Manager Søren Birk Rasmussen, Topsoe
Professor Jan-Dirk Grunwaldt, Karlsruhe Institute of Technology, Germany
Chairperson:
Associate Professor Susanne Mossin, DTU Chemistry