Self-templating construction of mesopores on three-dimensionally ordered macroporous La0.5Sr0.5MnO3 perovskite with enhanced performance for soot combustion

A three-dimensionally ordered macroporous (3DOM) La_0.5Sr_0.5MnO₃ perovskite was prepared by a colloidal crystal templating method, with extra mesopores created by selective dissolution method performed successively.

Storage and reduction of NOx by combining Sr-based perovskite catalyst with nonthermal plasma

A novel NO_x storage and reduction (NSR) system is developed for NO_x removal by integrating Sr-based perovskite catalyst with nonthermal plasma (NTP)-assisted process. In this hybrid system, Sr-based perovskite catalyst is applied for NO_x adsorption in the lean-burn condition while NTP is used as a desorption-reduction step to convert NO_x into N₂ under rich-burn condition. Innovative Sr-based perovskites including SrKMnCoO₄/BaO/Al₂O₃ (SKMCBA), SrKMnCeO₄/BaO/Al₂O₃ (SKMCeBA), and SrKCoNiO₄/BaO/Al₂O₃ (SKCNBA) are successfully prepared by impregnation method. Results indicate that SKMCBA possesses the highest NO_x trapped (214 μmole NO_x/g_catalyst) at 400 °C among 3 Sr-based perovskites investigated. High performance of SKMCBA for NO_x adsorption is mainly attributed to the addition of Mn and Co which own good oxidation ability. Further, SKMCBA is combined with NTP-assisted process for NO_x reduction. Result indicates that NO_x conversion achieved with NTP-assisted process reaches 83% with the applied voltage of 18 kV and frequency of 10 kHz in the absence of reducing agent. Additionally, various reducing agents including hydrogen (H₂), carbon monoxide (CO), and propene (C₃H₆) are introduced, individually, into the NTP reduction process, and the results indicate that performance of NSR with NTP can be effectively enhanced. Especially, 100% NO_x conversion is achieved with H₂-NTP. This study demonstrates that reduction of NO_x via NTP-assisted process is promising.

Active Site of O2 and Its Improvement Mechanism over Ce-Ti Catalyst for NH3-SCR Reaction

The current study on Ce-Ti catalyst was mainly focused on the function of NH3 and NO adsorption sites. In our study, by comparing Ce-Ti (doped catalyst) to Ce/Ti (supported catalyst), the active site of O2 and its improvement mechanism over Ce-Ti catalyst for NH3-Selective catalytic reduction (SCR) reactions were investigated. For Ce-Ti catalyst, a cerium atom was confirmed entering a TiO2 crystal lattice by X-ray diffraction (XRD) and Raman; the structure of Ce-□-Ti (□ represents oxygen vacancy) in Ce-Ti catalyst was confirmed by X-ray photoelectron spectroscopy (XPS) and Photoluminescence spectra (PL spectra). The nature of this structure was characterized by electron paramagnetic resonance (EPR), Ammonia temperature-programmed desorption (NH3-TPD), hydrogen temperature-programmed reduction (H2-TPR), Nitric oxide temperature-programmed desorption (NO-TPD) and In situ DRIFT. The results indicated that oxygen vacancies had a promotive effect on the adsorption and activation of oxygen, and oxygen was converted to superoxide ions in large quantities. Also, because of adsorption and activation of NO and NH3, electrons were transferred to adsorbed oxygen via oxygen vacancies, which also promoted the formation of superoxide ions. We expected that our study could promote understanding of the active site of O2 and its improvement mechanism for doped catalyst.

Carbothermal shock synthesis of high-entropy-alloy nanoparticles

The controllable incorporation of multiple immiscible elements into a single nanoparticle merits untold scientific and technological potential, yet remains a challenge using conventional synthetic techniques. We present a general route for alloying up to eight dissimilar elements into single-phase solid-solution nanoparticles, referred to as high-entropy-alloy nanoparticles (HEA-NPs), by thermally shocking precursor metal salt mixtures loaded onto carbon supports [temperature ~2000 kelvin (K), 55-millisecond duration, rate of ~105 K per second]. We synthesized a wide range of multicomponent nanoparticles with a desired chemistry (composition), size, and phase (solid solution, phase-separated) by controlling the carbothermal shock (CTS) parameters (substrate, temperature, shock duration, and heating/cooling rate). To prove utility, we synthesized quinary HEA-NPs as ammonia oxidation catalysts with ~100% conversion and >99% nitrogen oxide selectivity over prolonged operations.

Triple-shelled NiMn2O4 hollow spheres as an efficient catalyst for low-temperature selective catalytic reduction of NOx with NH3

Unique triple-shelled NiMn₂O₄ hollow spheres are fabricated by a facile solvothermal method.

Theoretical Study of Ripening Mechanisms of Pd Clusters on Ceria

We carried out density functional theory calculations to investigate the ripening of Pd clusters on CeO₂(111). Starting from stable Pd _n clusters (n = 1-21), we compared how these clusters can grow through Ostwald ripening and coalescence. As Pd atoms have mobility higher than that of Pd _n clusters on the CeO₂(111) surface, Ostwald ripening is predicted to be the dominant sintering mechanism. Particle coalescence is possible only for clusters with less than 5 Pd atoms. These ripening mechanisms are facilitated by adsorbed CO through lowering barriers for the cluster diffusion, detachment of a Pd atom from clusters, and transformation of initial planar clusters.

Controllable synthesis of Ce-doped α-MnO2for low-temperature selective catalytic reduction of NO

On account of the highly active exposed Mn atom on α-MnO₂with a mesoporous channel, the catalyst exhibits high performance for NH₃-based selective catalytic reduction of NO.

A comparative study of manganese–cerium doped metal–organic frameworks prepared via impregnation and in situ methods in the selective catalytic reduction of NO

Impregnation and in situ doping were applied for the preparation of MnCe loaded MOFs and the behavior of the catalysts in the SCR was investigated.

Preparation and application of effective different catalysts for simultaneous control of diesel soot and NOX emissions: An overview

Soot particulates and nitrogen oxides (NO_X) from diesel engine exhaust have been causing serious problems to human health and the global environment.

Combining nonthermal plasma with perovskite-like catalyst for NOx storage and reduction

A new NOx storage and reduction (NSR) system is developed for NOx removal by combining perovskite-like catalyst with nonthermal plasma technology. In this hybrid system, catalyst is mainly used for oxidizing NO to NO2 and storing them, while nonthermal plasma is applied as a desorption-reduction step for converting NOx into N2. An innovative catalyst with a high NOx storage capacity and good reduction performance is developed by successive impregnation. The catalysts prepared with various metal oxides were investigated for NOx storage capacity (NSC) and NOx conversion. Characterization of the catalysts prepared reveals that addition of cobalt (Co) and potassium (K) considerably increases the performance for NSC. Results also show that SrKMn0.8Co0.2O4 supported on BaO/Al2O3 has good NSC (209 μmol/gcatalyst) for the gas stream containing 500 ppm NO and 5 % O2 with N2 as carrier gas. For plasma reduction process, NOx conversion achieved with SrKMn0.8Co0.2O4/BaO/Al2O3 reaches 81 % with the applied voltage of 12 kV and frequency of 6 kHz in the absence of reducing agents. The results indicate that performance of plasma reduction process (81 %) is better than that of thermal reduction (64 %). Additionally, mixed gases including 1 % CO, 1 % H2 and 1 % CH4, and 2 % H2O(g) are simultaneously introduced into the system to investigate the effect on NSR with plasma system and results indicate that performance of NSR with plasma can be enhanced. Overall, the hybrid system is promising to be applied for removing NOx from gas streams. Graphical abstract ᅟ.

Surface Tuning of La0.5Sr0.5CoO3 Perovskite Catalysts by Acetic Acid for NOx Storage and Reduction

Selective dissolution of perovskite A site (A of ABO3 structure) was performed on the La1 - xSrxCoO3 catalysts for the NOx storage and reduction (NSR) reaction. The surface area of the catalysts were enhanced using dilute HNO3 impregnation to dissolve Sr. Inactive SrCO3 was removed effectively within 6 h, and the catalyst preserved the perovskite framework after 24 h of treatment. The tuned catalysts exhibited higher NSR performance (both NOx storage and NO-to-NO2 oxidation) under lean-burn and fuel-rich cycles at 250 °C. Large amounts of NOx adsorption were due to the increase of nitrate/nitrite species bonding to the A site and the growth of newly formed monodentate nitrate species. Nitrate species were stored stably on the partial exposed Sr(2+) cations. These exposed Sr(2+) cations played an important role on the NOx reduction by C3H6. High NO-to-NO2 oxidation ability was due to the generation of oxygen defects and Co(2+)-Co(3+) redox couples, which resulted from B-site exsolution induced by A-site dissolution. Hence, our method is facile to modify the surface structures of perovskite catalysts and provides a new strategy to obtain highly active catalysts for the NSR reaction.

Nonprecious mixed oxide catalysts Co3AlO and Co2NiAlO derived from nanoflowerlike cobalt-based hydrotalcites for highly efficient oxidation of nitric oxide

Nanoflowerlike Co3AlO-500 and Co2NiAlO-500 exhibit excellent NO oxidation performance upon abundant active sites Co³⁺/Ni³⁺–O_ads through formation of bridged bidentate nitrate.

Promotional effect and mechanism study of nonmetal-doped Cr/CexTi1−xO2 for NO oxidation: tuning O2 activation and NO adsorption simultaneously

Nonmetal-doped Cr/Ce_xTi_1−xO₂ was conductive to tune O₂ activation and NO adsorption strength simultaneously. Moreover, the catalytic mechanism was investigated for NO oxidation.

Promotional role of La addition in the NO oxidation performance of a SmMn2O5 mullite catalyst

A series of La_xSm_1−xMn₂O_δ (x = 0, 0.1, 0.3, 0.5) catalysts were synthesized through a co-precipitation method. The catalytic activity for NO oxidation was enhanced with La substitution, and the maximum activity was achieved at x = 0.3.

Oxygen vacancies on nanosized ceria govern the NOxstorage capacity of NSR catalysts

The oxygen vacancies on Pt/BaO/CeO₂govern the NO_xstorage capacity by creating efficient sites or channels for nitrate formation and its further transformation to Ba-based storage sites.

LaCoO3 perovskite in Pt/LaCoO3/K/Al2O3 for the improvement of NOx storage and reduction performances

A series of x wt% Pt/LaCoO₃/K/Al₂O₃ (x = 0, 0.3 and 1.0) were synthesized for NOx storage and reduction. 0.3 wt% Pt/LaCoO₃/K/Al₂O₃ shows higher NOx storage capacities, stronger SO₂ tolerance and better regenerability than 1.0 wt% Pt/K/Al₂O₃.

Nitrogen oxide removal over hydrotalcite-derived mixed metal oxides

Rigorous regulations of nitrogen oxide emissions require the development of technologies for their removal from exhaust gases.

The surface chemistry of NO(x) on mackinawite (FeS) surfaces: a DFT-D2 study

We present density functional theory calculations with a correction for the long-range interactions (DFT-D2) of the bulk and surfaces of mackinawite (FeS), and subsequent adsorption and dissociation of NO(x) gases (nitrogen monoxide (NO) and nitrogen dioxide (NO2)). Our results show that these environmentally important molecules interact very weakly with the energetically most stable (001) surface, but adsorb relatively strongly onto the FeS(011), (100) and (111) surfaces, preferentially at Fe sites via charge donation from these surface species. The NOx species exhibit a variety of adsorption geometries, with the most favourable for NO being the monodentate Fe-NO configuration, whereas NO2 is calculated to form a bidentate Fe-NOO-Fe configuration. From our calculated thermochemical energy and activation energy barriers for the direct dissociation of NO and NO2 on the FeS surfaces, we show that NO prefers molecular adsorption, while dissociative adsorption, i.e. NO2 (ads) → [NO(ads) + O(ads)] is preferred over molecular adsorption for NO2 onto the mackinawite surfaces. However, the calculated high activation barriers for the further dissociation of the second N-O bond to produce either [N(ads) and 2O(ads)] or [N(ads) and O2(ads)] suggest that complete dissociation of NO2 is unlikely to occur on the mackinawite surfaces.

MnO2 doped CeO2 with tailored 3-D channels exhibits excellent performance for NH3-SCR of NO

Due to a high surface area and 3-D meso-channels, the catalyst exhibits high performance for NH₃-SCR of NO.

A novel 3D oxide nanosheet array catalyst derived from hierarchical structured array-like CoMgAl-LDH/graphene nanohybrid for highly efficient NOx capture and catalytic soot combustion

A novel 3D oxide nanosheet array catalyst was fabricated using a graphene template induced strategy for highly efficient NO_x capture and catalytic soot combustion.

Structure–activity relationship of Cr/Ti-PILC catalysts using a pre-modification method for NO oxidation and their surface species study

Two Cr(vi) species are generated via pre-modification, which play the different roles in the catalytic reaction. That is, oxide state CrO₃ is beneficial to form the redox reaction with Cr₂O₃, and chromate with anionic form is adverse to accumulate SO₂ to improve their resistance.

Promotional effect of doping SnO2 into TiO2 over a CeO2/TiO2 catalyst for selective catalytic reduction of NO by NH3

The promotional effect of SnO₂ in a Ce/TiO₂ catalyst for NH₃-SCR reaction.

First principles investigation of NO2 and SO2 adsorption on γ-Al2O3 supported mono- and diatomic metal clusters

Atomistic simulations of NO₂ and SO₂ adsorption on γ-Al₂O₃ supported mono and diatomic clusters of Pt and Rh show that enhanced sulfur tolerance with respect to pristine metallic surfaces or extended nanoparticles, can be achieved.