Selective catalytic reduction of NOx with ammonia (NH3-SCR) over transition metal-based catalysts - influence of the catalysts support
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AGH University of Science and Technology
Publication date: 2019-09-26
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Agnieszka Szymaszek   

AGH University of Science and Technology
Physicochem. Probl. Miner. Process. 2019;55(6):1429–1441
Natural layered clays (bentonite and vermiculite) and natural zeolite (clinoptilolite) were tested and compared as the supports of the catalysts for selective catalytic reduction with ammonia (NH3-SCR). The raw materials were modified in order to improve their catalytic properties. Layered clays were treated with HNO3 and intercalated with Al2O3 pillars to enhance their acidity, porosity and specific surface area. Clinoptilolite was ion-exchanged with NH4NO3 in order to increase the content of Brönsted acid sites, indispensable for NH3 adsorption during the reaction. Subsequently, iron as an active phase was deposited on the modified supports by various methods, including incipient wetness impregnation, ion-exchange and co-precipitation. The efficiency of these methods was compared as NOx conversion obtained for each material. XRD analysis indicated that the initial modifications affected the structure of the raw aluminosilicates. FT-IR measurement confirmed the presence of characteristic Si-O and Al-O bonds and H2O molecules that occur naturally in the materials. UV-Vis spectroscopy results indicated that different types of Fe species were deposited on the catalysts surface and their form strongly depends on the type of the support. NH3-SCR catalytic tests showed that all of the analyzed materials exhibit satisfactory level of NO conversion and negligible concentration of by-product (N2O) in the exhaust gas. The highest catalytic activity (ca. 50% at 170°C and over 95% above 250°C) was obtained for Fe-Bent. The lowest concentration of N2O in the flue gas (less than 5 ppm in the whole temperature range) was observed for Fe-Clin.