Catalysts for low temperature conversion of nitrogen oxides

The objective of the present work is to prepare and characterize an appropriate catalyst system for low temperature removal and conversion of nitrogen oxides. The chosen catalyst preparation via chemical vapor infiltration is expected to introduce a higher infiltration load into these catalysts than common wet chemistry techniques. The support materials - commercially available activated carbon and zeolite - are infiltrated with iron, copper, manganese and their oxides. Structural characterization of the catalysts is performed with SEM, TEM, X-ray diffraction and low temperature nitrogen adsorption. The chemical composition is derived by means of EDX. Nitrogen oxide adsorption and decomposition properties are investigated in a recycle flow reactor. Micropores seem to have a significant effect on the catalytic activity. All investigated catalysts adsorb and convert nitrogen dioxide almost completely and the major conversion products are nitric oxide and nitrous oxide. The additional co-deposition of silica in activated carbon stabilizes the pore system during the catalysis process. Of all investigated zeolite-based catalysts, iron-infiltrated mordenite shows the largest nitrogen oxide conversion at 425 K and the largest release of oxygen and nitrogen as decomposition products. At low temperature, this catalyst is outperforming the synthesized carbon-based catalysts and even the well-characterized Cu-ZSM-5 catalyst.