Manganese oxide has been recognized as one of the most promising gaseous heterogeneous catalysts due to its low cost, environmental friendliness, and high catalytic oxidation performance. Mn-based ...oxides can be classified into four types: (1) single manganese oxide (MnOx), (2) supported manganese oxide (MnOx/support), (3) composite manganese oxides (MnOx-X), and (4) special crystalline manganese oxides (S-MnOx). These Mn-based oxides have been widely used as catalysts for the elimination of gaseous pollutants. This review aims to describe the environmental applications of these manganese oxides and provide perspectives. It gives detailed descriptions of environmental applications of the selective catalytic reduction of NOx with NH3, the catalytic combustion of volatile organic compounds, Hg0 oxidation and adsorption, and soot oxidation, in addition to some other environmental applications. Furthermore, this review mainly focuses on the effects of structure, morphology, and modified elements and on the role of catalyst supports in gaseous heterogeneous catalytic reactions. Finally, future research directions for developing manganese oxide catalysts are proposed.
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IJS, KILJ, NUK, PNG, UL, UM
MnOx/graphene composites were prepared and employed to enhance the performance of manganese oxide (MnOx) for the capture of elemental mercury (Hg(0)) in flue gas. The composites were characterized ...using FT-IR, XPS, XRD, and TEM, and the results showed that the highly dispersed MnOx particles could be readily deposited on graphene nanosheets via hydrothermal process described here. Graphene appeared to be an ideal support for MnOx particles and electron transfer channels in the catalytic oxidation of Hg(0) at a high efficiency. Thus, MnOx/graphene-30% sorbents exhibited an Hg(0) removal efficiency of greater than 90% at 150 °C under 4% O2, compared with the 50% removal efficiency of pure MnOx. The mechanism of Hg(0) capture is discussed, and the main Hg(0) capture mechanisms of MnOx/graphene were catalytic oxidation and adsorption. Mn is the main active site for Hg(0) catalytic oxidation, during which high valence Mn (Mn(4+) or Mn(3+)) is converted to low valence Mn (Mn(3+) or Mn(2+)). Graphene enhanced the electrical conductivity of MnOx, which is beneficial for catalytic oxidation. Furthermore, MnOx/graphene exhibited an excellent regenerative ability, and is a promising sorbent for capturing Hg(0).
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Abstract Capturing gaseous mercury (Hg 0 ) from sulfur dioxide (SO 2 )-containing flue gases remains a common yet persistently challenge. Here we introduce a low-temperature sulfur chemical vapor ...deposition (S-CVD) technique that effectively converts SO 2 , with intermittently introduced H 2 S, into deposited sulfur (S d 0 ) on metal sulfides (MS), facilitating self-sustained adsorption of Hg 0 . ZnS, as a representative MS model, undergoes a decrease in the coordination number of Zn–S from 3.9 to 3.5 after S d 0 deposition, accompanied by the generation of unsaturated-coordinated polysulfide species (S n 2– , named S d * ) with significantly enhanced Hg 0 adsorption performance. Surprisingly, the adsorption product, HgS (ZnS@HgS), can serve as a fresh interface for the activation of S d 0 to S d * through the S-CVD method, thereby achieving a self-sustained Hg 0 adsorption capacity exceeding 300 mg g −1 without saturation limitations. Theoretical calculations substantiate the self-sustained adsorption mechanism that S 8 ring on both ZnS and ZnS@HgS can be activated to chemical bond S 4 chain, exhibiting a stronger Hg 0 adsorption energy than pristine ones. Importantly, this S-CVD strategy is applicable to the in-situ activation of synthetic or natural MS containing chalcophile metal elements for Hg 0 removal and also holds potential applications for various purposes requiring MS adsorbents.
The selective removal and recovery of silver ions from an aqueous solution is necessary, owing to the toxicity, persistency, and recoverable value. Herein, we first reported that silver ions could be ...selectively removed from an acidic solution by utilizing redox-active covalent organic framework (COF) materials as an adsorbent, resulting in the loading of Ag nanoparticles (NPs) with a narrow size distribution onto the framework simultaneously. The redox-active COF not only showed promising performance in adsorbing silver ions but also had a high selectivity at a low pH value. Subsequently, it was found that the N sites of amine groups within the framework took responsibility for the Ag NP generation after the systematic investigation on the redox adsorption mechanism. Furthermore, the recycled Ag@COF materials could be further used as new adsorbents to remove Hg(II) ions from water via NPs as a “bridge”, exhibiting ultrahigh atomic utilization (>100%). Accordingly, this work not only provides a novel insight for the use of redox-active COF in the removal of metal ions but also opens a new field for designing of functionalized COF for their potential application in diverse areas.
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Abstract Ru single-atom catalysts have great potential to replace toxic mercuric chloride in acetylene hydrochlorination. However, long-term catalytic stability remains a grand challenge due to the ...aggregation of Ru atoms caused by over-chlorination. Herein, we synthesize an asymmetric Ru-In atomic pair with vinyl chloride monomer yield (>99.5%) and stability (>600 h) at a gas hourly space velocity of 180 h −1 , far surpassing those of the Ru single-atom counterparts. A combination of experimental and theoretical techniques reveals that there is a strong d - p orbital interaction between Ru and In atoms, which not only enables the selective adsorption of acetylene and hydrogen chloride at different atomic sites but also optimizes the electron configuration of Ru. As a result, the intrinsic energy barrier for vinyl chloride generation is lowered, and the thermodynamics of the chlorination process at the Ru site is switched from exothermal to endothermal due to the change of orbital couplings. This work provides a strategy to prevent the deactivation and depletion of active Ru centers during acetylene hydrochlorination.
•A new integrated process for the mercury removal and reclaim from the flue gas in the presence of SO2 was developed.•The laws of fate of mercury in Stage I of the integrated process were studied and ...revealed.•HgSO4 was determined as a more efficient absorbent on Hg0 removal and was introduced to Stage II of the integrated process.•1.0% H2O2 was introduced to the composite absorption solution to overcome the negative effect of SO2 on Hg0 removal in Stage II.
A new integrated process was developed for the removal and reclamation of mercury from the flue gas in the presence of SO2, typically derived from nonferrous metal smelting. The new process contains a pre-desulfurization unit (Stage I) and a co-absorption unit (Stage II). In Stage I, 90% of the SO2 from flue gas can be efficiently absorbed by ferric sulfate and reclaimed sulfuric acid. Meanwhile, the proportion of Hg2+ and Hg0 in the flue gas can be redistributed in this stage. Then, over 95% of the Hg0 and the residual SO2 can be removed simultaneously with a composite absorption solution from the flue gas in Stage II, which is much more efficient for the Hg0 reclaiming than the traditional method. The composite absorption solution in Stage II, which is composed of 0.1g/L HgSO4, 1.0% H2O2 and H2SO4, could effectively remove and reclaim Hg0 overcoming the negative effect of SO2 on Hg0 absorption. Moreover, the concentrations of HgSO4 and H2O2 were adjusted with the changes in of the concentrations of Hg0 and SO2 in the flue gas. It is a potential and promising technology for the mercury removal and reclaim from the flue gas in the presence of SO2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A Co–Mn binary metal oxide-modified layered MCM-22 zeolite was designed to capture gaseous elemental mercury (Hg
0
) from SO
2
-containing flue gas. The physicochemical properties of the Co–Mn/MCM-22 ...zeolite were characterized by XRD, FESEM, TEM, and XPS, and the results showed that MnO
2
was highly dispersed on the surface and in the channel of MCM-22 zeolite. Co
3
O
4
was loaded onto the surface of the MCM-22 zeolite via the stepwise ion exchange method to prevent SO
2
poisoning of the MnO
2
active site. The Hg
0
removal efficiency increased from 54 to 83% at 300 °C with 10% Co loading on the 5% Mn/MCM-22 zeolite when 200 ppm of SO
2
was introduced to the flue gas. The mechanism of Hg
0
removal was mainly associated with catalytic oxidation and chemisorption. Mn
4+
was the main active site for catalytic oxidation of Hg
0
to Hg
2+
, and the surface adsorbed oxygen re-oxidized Mn
3+
and combined with Hg
2+
to form Hg–O–Mn, in which Mn acted as a bridge. Co
3+
preferentially reacted with SO
2
to form CoSO
4
, thereby protecting the Mn active sites for Hg
0
capture. Therefore, Co–Mn/MCM-22 zeolite is a promising sorbent for the removal of Hg
0
and SO
2
resistance from SO
2
-containing flue gas.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The installation of electrostatic demisters (ESDs) makes possible the use of sorbent injection technology for recovering Hg
0
from non-ferrous smelting gas. ZnS, as a typical smelting raw material, ...could be a promising candidate due to the sulfur boding site for mercury. However, the low reaction rate and poor adsorption capacity limited its application. In this study, Co was incorporated into ZnS to enhance adsorption activity for recovering Hg
0
. Co
0.2
Zn
0.8
S exhibited the best Hg
0
capture performance among the modified sorbents. The Hg
0
adsorption capacity was up to 46.01 mg/g at 50 °C (with 50% breakthrough threshold), and the adsorption rate was as high as 0.017 mg/(g min). Meanwhile, SO
2
and H
2
O had no poison effects on Hg
0
adsorption. The chemical adsorption mechanism was proposed, which was Co
3+
, and sulfur active sites could immobilize Hg
0
in the form of stable HgS, following a Mars-Maessen reaction pathway. The spent sorbent will release ultrahigh concentration mercury-containing vapor through the heating treatment, which facilitated centralized recovery of Hg
0
. Meanwhile, inactivated sorbent can be used as smelting raw material to recover sulfur resources. Therefore, the control of Hg
0
emission from non-ferrous smelting gas by Co-adopted ZnS was cost-effective and did not form secondary pollution.
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•Develop a novel kind of mercury sorbent capable in a wider active temperature window.•SO2 tolerance of the sorbent is relative good at low temperature.•SO2 could strengthen the ...interaction between mercury and sorbent.•A mathematical model was built for calculation of mercury desorption activation energy.
A series of Sn–Mn binary metal oxides were prepared through co-precipitation method. The sorbents were characterized by powder X-ray diffraction (powder XRD), transmission electronic microscopy (TEM), H2-temperature-programmed reduction (H2-TPR) and NH3-temperature-programmed desorption (NH3-TPD) methods. The capability of the prepared sorbents for mercury adsorption from simulated flue gas was investigated by fixed-bed experiments. Results showed that mercury adsorption on pure SnO2 particles was negligible in the test temperature range, comparatively, mercury capacity on MnOx at low temperature was relative high, but the capacity would decrease significantly when the temperature was elevated. Interestingly, for Sn–Mn binary metal oxide, mercury capacity increased not only at low temperature but also at high temperature. Furthermore, the impact of SO2 on mercury adsorption capability of Sn–Mn binary metal oxides was also investigated and it was noted that the effect at low temperature was different comparing with that of high temperature. The mechanism was investigated by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs). Moreover, a mathematic model was built to calculate mercury desorption activation energy from Sn to Mn binary metal oxides.
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•The Co–Mn–Ti catalyst exhibited the highest activity and good stability for CH2Br2 oxidation.•The addition of Ti or Ti+Mn distorted the crystal structure and led to the formation of ...a Co–O–Ti solid solution.•The addition of Mn further enhanced the surface acidity and redox ability of the catalysts.•A plausible reaction mechanism for CH2Br2 oxidation over Co–Mn–Ti catalysts was proposed.
Co3O4 catalysts modified with Mn and Ti, prepared by co-precipitation method, were used for catalytic oxidation of dibromomethane (CH2Br2), a model molecule for brominated volatile organic compounds (BVOCs). Addition of Ti or Ti+Mn distorted the crystal structure and led to the formation of a Co–O–Ti solid solution. The addition of Mn further enhanced the surface acidity and redox ability of the catalysts. Co–Mn–Ti exhibited the highest activity with a T90 of approximately 234°C and the highest selectivity to CO2 at low temperatures. Additionally, Co–Mn–Ti showed good stability for at least 30h at 500ppm CH2Br2, 0 or 2 vol% H2O, 0 or 500ppm p-xylene (PX), and 10% O2 at a gas hourly space velocity of 60,000h−1, and the final products were COx, Br2, and HBr, without the formation of other Br-containing organic byproducts. This high catalytic activity was attributed to its high specific area, high surface acidity, and strong redox property. Furthermore, the synergetic effect of Co, Mn, and Ti made it superior for CH2Br2 oxidation. A plausible reaction mechanism for CH2Br2 oxidation over Co–Mn–Ti catalysts was proposed based on the analysis of the products and in situ diffuse-reflectance infrared Fourier transform spectroscopy results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
