Bifunctional YFeO 3-Based Catalysts Used in the Selective Catalytic Reduction of Nitrogen Monoxide in the Presence of Excess Oxygen

Abstract

The catalytic activity of YFeO 3-based catalysts in the lean-NO x process was studied for the sulfated perovskite YFeO 3, composites between YFeO 3 and the solid acid ZrO 2, as well as sulfated composites YFeO 3/ZrO 2. Moreover, a mechanical mixture between YFeO 3 and sulfated tetragonal zirconia (t-ZrO 2/SO 4) was studied. It is shown that the lean-NO x activity of YFeO 3 is improved by forming the composites YFeO 3/ZrO 2 as well as by sulfating samples, with the highest conversion rates of NO x into N 2 being about 30% at about 400°C. The disadvantage of these materials is that the activity decreases with increasing the oxygen content of the feed gas. However, the mechanical mixture between YFeO 3 and t-ZrO 2/SO 4 shows not only an improved high-temperature activity at about 400°C but also a pronounced low temperature (<300–350°C) activity. The latter clearly increases with increasing oxygen content, whereas the former decreases. The opposing effect of oxygen is explained by different reaction mechanisms.