SSZ-13-supported manganese oxide catalysts for low temperature selective catalytic reduction of $$\hbox {NO}_{\mathrm{x}}$$ NO x by $$\hbox {NH}_{3}$$ NH 3

The protective effect of biomineralized BSA-Mn3O4 nanoparticles on HUVECs investigated by atomic force microscopy

BSA-Mn3O4 nanoparticles were successfully synthesized by one-step biomineralization method, the mechanism of antioxidant activity of BSA-Mn3O4 nanoparticles in HUVECs was investigated from the perspective of biomechanics.

Coal bottom ash derived zeolite (SSZ-13) for the sorption of synthetic anion Alizarin Red S (ARS) dye

SSZ-13 zeolite was successfully synthesized from coal bottom ash (CBA) upon hydrothermal treatment for selective sorption of Alizarin Red S (ARS) dye. The characterization of CBA, and SSZ-13 were performed using BET, SEM, FTIR, XRF, and XRD techniques. The optimal fusion ratio (CBA: NaOH) was identified as 1:3, resulting zeolite SSZ-13 with a specific surface area of 206.6 m²/g, compared to raw CBA (7.81 m²/g). The kinetics, isotherms, and thermodynamics of the ARS adsorption onto the SSZ-13, and CBA were assessed under various conditions. The results indicated that the adsorption phenomenon is optimal under acidic medium (pH = 2 for CBA, pH = 3 for SSZ-13); at ambient room temperature of 298 K; adsorbent dosage of 0.03 g, contact time of 120 min. Further, the equilibrium data fitted well to Langmuir isotherm (q_e = 210.75 mg/g), following pseudo-second-order kinetics. Moreover, the chemisorption phenomenon is clearly described using Elovich kinetic model. Various thermodynamic parameters signifies the adsorption phenomenon is spontaneous, and endothermic in nature. Finally, regeneration studies revealed the sensitivity of SSZ-13 zeolite towards 0.1 M NaOH/EtOH eluent in recovery and the possibility of reuse to five successive adsorption/desorption cycles. Thus, hydrothermal treatment of CBA has potential in producing zeolites suitable to adsorption.

Soot Combustion over Niobium-Doped Cryptomelane (K-OMS-2) Nanorods—Redox State of Manganese and the Lattice Strain Control the Catalysts Performance

A series of Nb-doped (0–23 wt%) cryptomelane catalyst (Nb-K-OMS-2) was synthesized and thoroughly characterized by XRD, TEM/EDX, XRF, XPS, XAS, UV-Vis, and Raman techniques corroborated by the work function measurements. The obtained catalysts were tested for soot oxidation (Printex U) in model tight and loose contact modes. It was shown that the catalytic properties of the Nb-K-OMS-2 are controlled by the amount of Nb dopant in a strongly non-monotonous way. The introduction of niobium gives rise to the strain in the cryptomelane lattice, accompanied by significant Mn+3/Mn+4 ratio variations and concomitant work function changes. The isotopic exchange experiments revealed that the catalytic activity of the Nb-OMS-2 catalysts in soot combustion proceeds via the pathways, where both the activated suprafacial 18O and the surface 16O2− species participate together in the reaction. The niobium doping level controls the non-monotonous changes of the catalyst work function and the lattice strain, and variations of these parameters correlate well with the observed deSoot activity. To our best knowledge, the role of the lattice strain of the cryptomelane catalysts was documented for the first time in this study.

Promoting Effect of Mn on In Situ Synthesized Cu-SSZ-13 for NH3-SCR

The effect of Mn impregnation on the NH3-SCR (selective catalytic reduction of NOx by NH3) activity of in situ synthesized Cu-SSZ-13 was investigated in this work. It was found that Mn addition could efficiently improve the low-temperature activity of Cu-SSZ-13. The optimal amount of Mn was 5 wt.%, and NOx conversion was improved by more than 20% over a temperature range of 120 °C to 150 °C. SEM (scanning electron microscopy), XRD (X-ray diffraction), N2 adsorption-desorption, H2-TPR (temperature programmed reduction of H2), NH3-TPD (temperature programmed desorption of NH3) and in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) experiments were conducted to investigate the changes in the zeolite structure, active sites, acid sites and reaction mechanism. The impregnated MnOx species caused a decline in the crystallinity of Cu-SSZ-13 but markedly improved the redox ability. Nitrate and nitrite species were observed in the Mn-modified Cu-SSZ-13, and the formation of these species was thought to cause the observed increase in low-temperature NH3-SCR activity. The results show that the addition of Mn is a promising method for promoting the low-temperature catalytic activity of Cu-SSZ-13.

Production of an effective catalyst with increased oxygen vacancies from manganese slag for selective catalytic reduction of nitric oxide

Manganese slag is a solid waste produced by the steel industry and usually lacks a proper recycling. In this paper, the manganese slag was used to synthesize a catalyst via microwave assistant method and applied in selective catalytic reduction of nitric oxide. As a result, the catalyst exhibited an excellent low-temperature activity. It removed 78.31% of nitric oxide at 100 °C, 44.44% higher than that of a slag-derived catalyst synthesized by ammonia impregnation, and 63.18% higher than that of a commercial catalyst. Even after a hydrothermal treatment, the catalyst still showed a removal of 69.26% at 150 °C. After a detailed characterization, the low-temperature activity was attributed to an increased amount of oxygen vacancies, which were generated during the microwave synthesis. The generated oxygen vacancies provided adsorption sites for chemisorbed oxygens, which then promoted the electron transfer for reduction of nitric oxide. The main result of this work will help to develop a low-cost catalyst and obtain a high-value-added utilization of manganese slag at the same time.

Co-Exchange of Mn: A Simple Method to Improve Both the Hydrothermal Stability and Activity of Cu–SSZ-13 NH3–SCR Catalysts

A series of Cu–Mn–SSZ-13 catalysts were obtained by co-exchange of Mn and Cu into SSZ-13 together (ion exchange under a mixed solution of Cu(NO3)2 and Mn(NO3)2) and compared with Cu–SSZ-13 catalysts on the selective catalytic reduction (SCR) of nitric oxide (NO) by ammonia. The effects of total ion exchange degree and the effect of Mn species on the structure and performance of catalysts before and after hydrothermal aging were studied. All fresh and aged catalysts were characterized with several methods including temperature-programmed desorption with NH3 (NH3-TPD), X-ray diffraction (XRD), 27Al and 29Si solid-state nuclear magnetic resonance (NMR), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and low-temperature N2 adsorption–desorption techniques. The results showed that the increase of the total ion exchange degree can reduce the content of residual Brønsted acid sites of catalysts, thus relieved the dealumination and the decrease of crystallinity of the catalyst during hydrothermal aging. The moderate addition of a Mn component in Cu–Mn–SSZ-13 catalysts significantly increased the activity of NO conversion at low temperature range. The selected Cu(0.2)Mn(0.1)–SSZ-13 catalyst achieved a high NO conversion of >90% in the wide and low temperature range of 175–525 °C and also exhibited good N2 selectivity and excellent hydrothermal stability, which was related to the inhibition of the Mn component on the aggregation of Cu species and the pore destruction of the catalyst during hydrothermal aging.