Selective Catalytic Reduction of NOx over Perovskite-Based Catalysts Using CxHy(Oz), H2 and CO as Reducing Agents—A Review of the Latest Developments

Abstract

Selective catalytic reduction (SCR) is probably the most widespread process for limiting NOx emissions under lean conditions (O2 excess) and, in addition to the currently used NH3 or urea as a reducing agent, many other alternative reductants could be more promising, such as CxHy/CxHyOz, H2 and CO. Different catalysts have been used thus far for NOx abatement from mobile (automotive) and stationary (fossil fuel combustion plants) sources, however, perovskites demand considerable attention, partly due to their versatility to combine and incorporate various chemical elements in their lattice that favor deNOx catalysis. In this work, the CxHy/CxHyOz−, H2−, and CO-SCR of NOx on perovskite-based catalysts is reviewed, with particular emphasis on the role of the reducing agent nature and perovskite composition. An effort has also been made to further discuss the correlation between the physicochemical properties of the perovskite-based catalysts and their deNOx activity. Proposed kinetic models are presented as well, that delve deeper into deNOx mechanisms over perovskite-based catalysts and potentially pave the way for further improving their deNOx efficiency.

Fe-CP-based Catalytic Oxidation and Dissipative Self-Assembly of a Ferrocenyl Surfactant Applied in DNA Capture and Release

“…The mass spectra of FTMBr (Figure S1D) also confirmed this result. As shown in Figure S1A, the electron gain and loss of FTMBr lay the foundation for redox reactions. − This switchable process can be realized by redox stimuli as oxidizing/reducing agents or electrochemical methods. The method of carrying out simple and convenient catalytic oxidation of ferrocene plays an important role in the development of the redox properties of ferrocene.…”

Methane Catalytic Combustion under Lean Conditions over Pristine and Ir-Loaded La1−xSrxMnO3 Perovskites: Efficiency, Hysteresis, and Time-on-Stream and Thermal Aging Stabilities

“…On the other hand, mixed metal oxides, especially those of the perovskite class (ABO 3 ), combine high thermal and chemical stabilities with the adequate activity of oxidation reactions, while keeping their cost relatively low [42][43][44][45][46]. Perovskites based on the combination of La and Mn in the A and B sites, respectively, are among the most popular materials in the family.…”

“…Perovskites based on the combination of La and Mn in the A and B sites, respectively, are among the most popular materials in the family. The partial substitution of La 3+ by Sr 2+ in the perovskite structure (i.e., La 1−x Sr x MnO 3 ) can enhance the redox properties of the material by increasing the oxygen vacancies and the oxidation state of the B cation (Mn), introducing significant changes to their catalytic performance and their thermal stability [42][43][44][45][46][47][48][49]. Especially after the inspiring discovery of Nishihata et al [50] and Tanaka et al [51], who demonstrated the self-regenerative function of noble metal substituted perovskites, a phenomenon that was later called "redox exclusion" [52,53], as well as methods that determine the nanostructure of the perovskite itself, thus improving the surface area and other catalysisrelated properties [54,55], new horizons were opened for the use of perovskites in various environmental- [54,[56][57][58][59] and energy- [55,[60][61][62][63][64] related catalytic processes, which resulted in great success.…”

“…However, the classical partial substitution of the A and/or B sites of an ABO 3 perovskite with other cations, with the same or different valences, to obtain substituted (as called) A 1−y A'yB 1−x B' x O 3±δ perovskites, remains a popular methodology for controlling the performance of perovskites due to its high flexibility. The bulk, surface, and redox properties of the original ABO 3 perovskite can be easily tailored on demand [43][44][45][46][47]. Emphasis is always placed on the oxygen storage capacity (OSC), oxygen ion mobility, and population of the surface oxygen vacancies (O defects) of the substituted perovskites; these properties play a key role in catalysis via oxides [56][57][58][59][60][61][62][63][64][65][66][67], as well as in catalysis via dispersed metal nanoparticles on oxide supports [13][14][15][68][69][70][71][72][73][74][75].…”

Comparative Analysis of NOx Emission Reduction in Engines Using NiCo2O4 Nanoparticles without External Reductant at Low Temperatures: An Experimental Investigation

“…For SCR NOx reduction, a variety of catalysts have been studied, including platinum group metals (PGM), perovskite-type oxides, spinel-type oxides, and mixed transition metal oxides [12][13][14][15]. In a low-temperature selective catalytic reduction, low-cost spinels were used [16].…”