Single-stage synthesis of highly dispersed copper and iron oxides on mesoporous supports for NH3-SCR

Abstract

Selective catalytic reduction (SCR) of nitrogen oxides (NOx) is a process where NOx is reduced to nitrogen (N2) by use of a reducing agent. One common reducing agent is ammonia (NH3-SCR). Increasingly stricter regulation on NOx emissions in the transportation sector creates a demand for efficient SCR catalysts. In this work, a design strategy for metal oxide supported NH3-SCR catalysts has been explored. A sol-gel synthesis using micellular structure directing agents was used to synthesize copper (Cu) and iron (Fe) catalysts supported on mesoporous alumina (Al2O3) and zirconia (ZrO2). The resulting catalysts were found to have near-atomic dispersion of Cu and Fe at high metal loading. Bimetallic Fe-Cu/ZrO2 catalysts were also synthesized in the same manner. The samples were characterized using N2 physisorption, XRD, SEM, TEM and XAS. NH3-SCR tests were performed at steady state in a fixed bed reactor. The synthesis method was found to be a simple, efficient and reliable method to produce well dispersed catalysts supported on Al2O3 and ZrO2. TEM and XAS results indicated high metal dispersion up to 15 wt% metal loading. Increasing the metal loading while maintaining the dispersion led to higher conversion rates of NO due to higher active site density of the catalyst. Bimetallic Fe-Cu/ZrO2 catalysts were found to have higher conversion rates at low and high temperature than their monometallic counterparts, indicating the combination of active sites provided low temperature activity from Cu and high temperature activity from Fe. It was observed that the presence of H2O in the reactor feed had a deactivating effect on all tested catalysts, particularly on Cu/ ZrO2, while ZrO2-supported catalysts were more resistant. The deactivating effect of H2O is a drawback that any further development should seek to mitigate. The high site density, and potential for combining the advantages of Cu and Fe active sites are advantages that could be utilized. Further optimisation and development is required before these catalysts are relevant for practical applications.