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, NO 2 ) or N 2 O 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 N 2 O 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 (NH 3 -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 (deN 2 O) and selective catalytic reduction of N 2 O (N 2 O-SCR). Finally, the remaining challenges and future trends are highlighted.

Silver‐Doped Cobalt (Magnesium) Aluminum Mixed Metal Oxides as Potential Catalysts for Nitrous Oxide Decomposition

“…Despite intensive research on suitable technologies for N 2 O abatement, targeted catalyst development in which the effects of inhibiting compounds are considered is limited. Co‐containing, hydrotalcite‐derived mixed metal oxides are one of the most efficient catalysts for N 2 O decomposition (deN 2 O) . In early studies, Kannan and Swamy investigated several combinations of M 2+ /Mg, Co, Ni, Cu, or Zn and M 3+ /Al, Fe, or Cr together with different M 2+ /M 3+ molar ratios.…”

“…found that the presence of Mg in CoMgAl‐O x (Co/Mg/Al=2:1:1, 1:2:1 mol %) improved the textural properties of the materials and eliminated the initial deactivation of the catalysts in the presence of SO 2 and O 2 . Furthermore, the incorporation of noble metals, especially Rh with 0.7 wt % loading, within the brucite‐like layers of the precursors led to the superior activity of mixed metal oxides; however, their high cost (rhodium nitrate was the most efficient precursor) limits their applicability . Furthermore, Ag‐doped materials have been investigated extensively for the selective oxidation of methanol, the epoxidation of ethylene, and the selective catalytic reduction (SCR) of NO x , whereas their use in N 2 O reduction or decomposition remains relatively rare.…”

“…Extensive research has been reported for Co‐containing mixed metal oxides for deN 2 O . However, reports on Ag‐promoted Co‐containing materials are limited.…”

Enhanced Oxygen Vacancies in a Two-Dimensional MnAl-Layered Double Oxide Prepared via Flash Nanoprecipitation Offers High Selective Catalytic Reduction of NOx with NH3

“…Two-dimensional layered double hydroxide (LDH)-derived MMOs have recently attracted widespread attention because of their special two-dimensional structures, higher active sites, and specific surface areas [22,23,24]. For example, two-dimensional (2D) Co-Al MMOs that are derived from LDH have been investigated as a potential catalyst for NO x removal at high temperatures of 750 °C in the presence of oxygen and water [25].…”

Low Temperature Selective Catalytic Reduction (SCR) of NOx Emissions by Mn-doped Cu/Al2O3 Catalysts

“…The commercial catalysts V2O5-WO3/TiO2 and V2O5-WO3 (MO3)/TiO2 were widely used as NH3-SCR in stationary engines exhaust, encounter difficulties such as ammonia slip, air heater fouling, ammonium sulfate deposition and being hazardous not a good choice for vehicular engines. Cu-ZSM-5 and Fe-ZSM-5 are highly active and stable at high temperatures but hydrothermally unstable make them not viable for commercial applications [14].…”