Nitrogen oxide removal over hydrotalcite-derived mixed metal oxides

Abstract

Rigorous regulations of nitrogen oxide emissions require the development of technologies for their removal from exhaust gases. Implementation of appropriate catalysts can potentially promote NO_x (NO, NO₂) or N₂O removal in shorter reaction time and under milder operation conditions. However, several challenges have to be faced upon trying to address nitrogen oxide pollution with catalytic systems such as sufficient catalytic performance, suitable operational temperatures and catalyst poisoning. The flexible structure of hydrotalcite-like compounds offers the opportunity to introduce various metals into the materials to provide active and selective catalysts for NO_x and N₂O removal. This minireview summarizes the abatement of nitrogen oxides by using hydrotalcite-derived mixed metal oxides. At first, a brief overview on the general features of hydrotalcite-originated mixed metal oxides and their applications in catalysis is provided. Later on, the application of mixed metal oxides as SCR catalysts with both ammonia (NH₃-SCR) and hydrocarbons (HC-SCR) as reducing agents is discussed. An overview of the mixed metal oxides applied as catalysts for NO_x storage/reduction (NSR) and further in the simultaneous removal of NO_x and soot particles is provided. Additionally, this review discusses mixed metal oxides as efficient catalysts for catalytic decomposition (deN₂O) and selective catalytic reduction of N₂O (N₂O-SCR). Finally, the remaining challenges and future trends are highlighted.