Perovskite-Based Catalysts as Efficient, Durable, and Economical NOx Storage and Reduction Systems

Abstract

Diesel engines operate under net oxidizing environment favoring lower fuel consumption and CO2 emissions than stoichiometric gasoline engines. However, NOx reduction and soot removal is still a technological challenge under such oxygen-rich conditions. Currently, NOx storage and reduction (NSR), also known as lean NOx trap (LNT), selective catalytic reduction (SCR), and hybrid NSR–SCR technologies are considered the most efficient control after treatment systems to remove NOx emission in diesel engines. However, NSR formulation requires high platinum group metals (PGMs) loads to achieve high NOx removal efficiency. This requisite increases the cost and reduces the hydrothermal stability of the catalyst. Recently, perovskites-type oxides (ABO3) have gained special attention as an efficient, economical, and thermally more stable alternative to PGM-based formulations in heterogeneous catalysis. Herein, this paper overviews the potential of perovskite-based formulations to reduce NOx from diesel engine exhaust gases throughout single-NSR and combined NSR–SCR technologies. In detail, the effect of the synthesis method and chemical composition over NO-to-NO2 conversion, NOx storage capacity, and NOx reduction efficiency is addressed. Furthermore, the NOx removal efficiency of optimal developed formulations is compared with respect to the current NSR model catalyst (1–1.5 wt % Pt–10–15 wt % BaO/Al2O3) in the absence and presence of SO2 and H2O in the feed stream, as occurs in the real automotive application. Main conclusions are finally summarized and future challenges highlighted.

Analyzing the role of copper in the soot oxidation performance of BaMnO3-perovskite-based catalyst obtained by modified sol-gel synthesis

“…391 NO X -TPR tests are useful to determine the catalytic activity for NO x adsorption/desorption process (Figure 9) and NO to NO 2 oxidation (Figure 10). In Figure 9, the NO x conversion profiles reveal that the BMC3-CX catalysts calcined at low temperatures (between 600ºC and 750ºC) show some adsorption/desorption capacity, which is low if it is compared with the corresponding to active catalysts for NO x storage, as Ba 1-y A y Ti 1-x Cu x O 3 [63,64], BaFeO 3 [65] or La 1-y A y CoO 3 [66] . Although the NO x adsorption capacity is low, it must be considered that, for the BMC3-C600, BMC3-C700 and BMC3-C750 samples, the NO 2 generation profiles (Figure 10) do not show the total amount of the generated NO 2 , it only shows the not adsorbed one.…”

Oxidation and Storage Mechanisms for Nitrogen Oxides on Variously Terminated (001) Surfaces of SrFeO3−δ and Sr3Fe2O7−δ Perovskites

“…Consequently, developing environmental catalysts with only base metal elements is an urgent issue. Thus, the interest in researching perovskite-type oxides with the chemical formula ABO 3 has been growing in recent years. − …”

Promotion of A-Site Ag-Doped Perovskites for the Catalytic Oxidation of Soot: Synergistic Catalytic Effect of Dual Active Sites

“…The perovskite structure can tolerate the partial replacement of cations at the A and/or B position by other cations. Hence, its electronic structure and corresponding catalytic activity can be adjusted to optimize the redox and oxygen migration properties. − Although the redox property of the perovskite depends strongly on the transition-metal elements at the B-site, modification of the A site also affects its activity . It was reported that the replacement of the A site could change the crystal structure and lead to total charge imbalance at the B-site, , accompanied by the creation of oxygen vacancies .…”