Research paperEngineering of crystal phase over porous MnO2 with 3D morphology for highly efficient elimination of H2S
Graphical Abstract
Introduction
Hydrogen sulfide (H2S) is an extremely odorous and nocuous gas responsible for facilities corrosion and catalysts poisoning in industry applications (Shah et al., 2017, Chen et al., 2020, Cao et al., 2019). The Claus technology is a traditional utilized method for the removal of H2S. Nevertheless, 2–5% of H2S cannot be converted to S owing to thermodynamic limitations (Pan et al., 2020, Li et al., 2020). Among advanced desulfurization approaches, the selective oxidation process (2H2S+O2 → (2/n)Sn + 2H2O) is a highly appealing technology due to thermodynamic completeness and low capital requirement (Zheng et al., 2019, Zhang et al., 2015, Lei et al., 2019).
With abundant oxygen vacancies, excellent redox ability and specific physical/chemical properties including diverse oxidation states and crystal structures, manganese dioxide (MnO2) has been extensively investigated in the field of pollution control (Hayashi et al., 2019, Zhang et al., 2017). Mn-based materials can also be considered for the H2S selective oxidation. Shin et al. concluded that the considerable activities of H2S selective oxidation over MnVOx catalyst are due to the promoted redox property by adding MnO2 (Shin et al., 2001). Nevertheless, the Mn-based catalysts are unsatisfactory because of poor porosity and easy sulfation. During H2S oxidation reaction, the deposition of sulfur and sulfate on the catalyst with poor porosity would cause the blocking of active sites and pores, resulting in low stability and activity.
Crystal-phase engineering is regarded as a knob to induce various physico-chemistry properties in metal oxides (Hu et al., 2019, Cheng et al., 2019). This is particularly true for MnO2-based catalysts due to the crystal structure of MnO2 plays a crucial role in determining the defect sites (Chen et al., 2020). Intrinsically, crystalline MnO2 usually exists in many polymorphic forms, mainly including δ-, β-, and α-type. The MnO2 nanocrystals consist of [MnO6] octahedral units shared by edges or corners, which leads to different layered and tunnel structures. The synergism of defect sites and different structures promotes the crystal-phase dependence of catalytic reactivity over MnO2-based catalysts (Xu et al., 2017). Zhang et al. concluded that δ-MnO2 is superior to other crystal phase of MnO2 with respect to the formaldehyde oxidation due to special 2D layer tunnel structure (Zhang et al., 2015). Yan et al. reported that the interaction between Mn2+/Mn3+ and Hg2+ is responsible for the Hg0 oxidation, and the activities increased as follow: β-MnO2 < γ-MnO2 < α-MnO2 (Xu et al., 2015). As for the catalytic oxidation of H2S, oxygen vacancies and reducibility of MnO2 could be controlled by crystal-phase engineering, which leads to higher oxygen concentration and therefore promotes catalytic activity. In addition, the adsorption energy of by-product SO2 is highly dependent on the crystal types of MnO2, which is beneficial to alleviating the formation of sulfate and therefore improves the stability (Ye et al., 2020). Although various studies have focused on phase dependence of catalytic performance over MnO2, the application of MnO2 in H2S selective oxidation is rare and relationship between crystalline phases of manganese dioxide and its catalytic activity has not been explored.
Toward this end, α-, β- and δ-MnO2 samples with hierarchical porous structures were successfully prepared by a facile oxalate approach. The decomposition of oxalate during the calcination process leads to the generation of hierarchical porous structure. Compared with α- and β-MnO2, the porous δ-MnO2 nanospheres displays better activity, S yield, and stability in H2S oxidation. The hierarchical porous structure consisted of at least two levels of porosity is beneficial to the reaction. We elaborately explored the impact of crystal phase, redox ability, and oxygen vacancy on the catalytic performance of MnO2. Electron energy-loss spectroscopy (EELS) spectra were also conducted to get insight into intrinsic oxygen vacancy. Moreover, the reaction pathway and structure-activity relationship for catalytic oxidation of H2S over Mn-based catalysts were revealed by the combination of the advanced characterizations.
Section snippets
Synthesis of porous δ-MnO2
In a typical procedure, 40 mL of KMnO4 (0.16 M) aqueous solution and 90 mL of (NH4)2C2O4·H2O (0.036 M) were mixed in a beaker (150 mL) under magnetic stirring at 50 °C for 30 min. Then the solution was transformed into an autoclave (200 mL) and kept at 205 °C for 24 h. After cooled down, the precipitate was centrifuged and washed with distilled water for several times. Finally, the precipitate was dried under vacuum in an oven at 95 °C overnight with the calcination at 300 °C for 2 h.
Synthesis of porous α-MnO2
40 mL of
Structural properties and morphology
The XRD patterns displayed in Fig. 1A indicate that the MnO2 samples with different phase structures were successfully prepared by the adopted hydrothermal methods. δ-MnO2 shows diffraction peaks at 2θ = 12.2, 24.7, 36.4 and 65.4°, which are assigned to the (001), (002), (100), and (110) planes of birnessite structure of hexagonal phase (JCPDS 80-1098, C2/m) with poor crystallinity (Sun et al., 2016). The diffraction peaks at 2θ = 12.8, 18.1, 28.7, 37.6, 41.9, 49.8, 56.4, 60.4 and 69.5°
Conclusions
In summary, the crystal-phase dependence of H2S selective oxidation over porous α-, β- and δ-MnO2 catalysts was systematically studied. The structure-property relationships established in this work prove that the porous δ-MnO2 nanospheres possesses large number of oxygen vacancies (verified by XPS, EELS, and EPR spectra) that favors more oxygen to be adsorbed on the catalyst and further transforms to active oxygen. As a result, δ-MnO2 showed the highest reactivity for catalytic oxidation of H2S
CRediT authorship contribution statement
Shijing Liang, Lijuan Shen and Lilong Jiang conceived the research and supervised the project. Xiaohai Zheng, Zheng Yao and Yong Zheng performed the experiments, Xiaohai Zheng wrote the paper, Yihong Xiao and Yanning Cao analyzed the data. All authors discussed the results and commented on the manuscript.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors are grateful to the financial support from National Natural Science Foundation of China (22078063, 21677036 and 21878052), the National Key Research and Development Program of China (2018YFA0209304) and the Natural Science Foundation of Fujian Province (2018J01693 and 2020H6007).
References (76)
- et al.
Screening of catalysts for H2S abatement from biogas to feed molten carbonate fuel cells
Int. J. Hydrog. Energy
(2013) - et al.
Ammonium-treated birnessite-type MnO2 to increase oxygen vacancies and surface acidity for stably decomposing ozone in humid condition
Appl. Surf. Sci.
(2019) - et al.
Highly effective direct decomposition of H2S by microwave catalysis on core-shell Mo2N-MoC@SiO2 microwave catalyst
Appl. Catal. B Environ.
(2020) - et al.
In-situ DRIFTS for the mechanistic studies of NO oxidation over α-MnO2, β-MnO2 and γ-MnO2 catalysts
Chem. Eng. J.
(2017) - et al.
Effects of surface physicochemical properties on NH3-SCR activity of MnO2 catalysts with different crystal structures
Chin. J. Catal.
(2017) - et al.
Potassium-modulated δ-MnO2 as robust catalysts for formaldehyde oxidation at room temperature
Appl. Catal. B: Environ.
(2020) - et al.
Porous nanosheets of carbon-conjugated graphitic carbon nitride for the oxidation of H2S to elemental sulfur
Carbon
(2019) - et al.
Isolated iron sites embedded in graphitic carbon nitride (g-C3N4) for efficient oxidative desulfurization
Appl. Catal. B Environ.
(2020) - et al.
Efficient catalytic elimination of COS and H2S by developing ordered mesoporous carbons with versatile base N sites via a calcination induced self-assembly route
Chem. Eng. Sci.
(2020) - et al.
Facile and green synthetic strategy of birnessite-type MnO2 with high efficiency for airborne benzene removal at low temperatures
Appl. Catal. B Environ.
(2019)
Highly efficient mesoporous MnO2 catalysts for the total toluene oxidation: Oxygen-Vacancy defect engineering and involved intermediates using in situ DRIFTS
Appl. Catal. B: Environ.
Probing the room-temperature oxidative desulfurization activity of three-dimensional alkaline graphene aerogel
Appl. Catal. B Environ.
Hierarchically porous γ-Al2O3 nanosheets: facile template-free preparation and reaction mechanism for H2S selective oxidation
Chem. Eng. J.
Development of vanadium-based mixed oxide catalysts for selective oxidation of H2S to sulfur
Appl. Catal. B Environ.
Au/Rod-like MnO2 catalyst via thermal decomposition of manganite precursor for the catalytic oxidation of toluene
Catal. Today
Boosted crystalline/amorphous Fe2O3–δ core/shell heterostructure for flexible solid-state pseudocapacitors in large scale
Nano Energy
Selective catalytic oxidation of H2S to elemental sulfur over titanium based Ti–Fe, Ti–Cr and Ti–Zr catalysts
Int. J. Hydrog. Energy
The effect of manganese vacancy in birnessite-type MnO2 on room-temperature oxidation of formaldehyde in air
Appl. Catal. B-Environ.
Insight into the mesoporous FexCe1−xO2−δ catalysts for selective catalytic reduction of NO with NH3: regulable structure and activity
J. Catal.
EELS analysis of cation valence states and oxygen vacancies in magnetic oxides
Micron
Structural effect and reaction mechanism of MnO2 catalysts in the catalytic oxidation of chlorinated aromatics
Chin. J. Catal.
Design of 3D MnO2/Carbon sphere composite for the catalytic oxidation and adsorption of elemental mercury
J. Hazard. Mater.
Different crystal-forms of one-dimensional MnO2 nanomaterials for the catalytic oxidation and adsorption of elemental mercury
J. Hazard. Mater.
Comparative study of α-, β-, γ-and δ-MnO2 on toluene oxidation: oxygen vacancies and reaction intermediates
Appl. Catal. B: Environ.
Insights into the surface-defect dependence of molecular oxygen activation over birnessite-type MnO2
Appl. Catal. B Environ.
Effect of χ-alumina addition on H2S oxidation properties of pure and modified γ-alumina
Chin. J. Catal.
Effect of manganese dioxide crystal structure on adsorption of SO2 by DFT and experimental study
Appl. Surf. Sci.
Insight into the H2S selective catalytic oxidation performance on well-mixed Ce-containing rare earth catalysts derived from MgAlCe layered double hydroxides
J. Hazard. Mater.
Insight into the effect of oxygen species and Mn chemical valence over MnOx on the catalytic oxidation of toluene
Appl. Surf. Sci.
Synthesis and application of highly dispersed ordered mesoporous silicon-doped Pd-alumina catalyst with high thermal stability
Chem. Eng. J.
Promoting effect of Cu-doping on catalytic activity and SO2 resistance of porous CeO2 nanorods for H2S selective oxidation
J. Catal.
Insight into the effect of morphology on catalytic performance of porous CeO2 nanocrystals for H2S selective oxidation
Appl. Catal. B-Environ.
Design, synthesis and characterization of vanadia-doped iron-oxide pillared montmorillonite clay for the selective catalytic oxidation of H2S
Dalton Trans.
Low temperature H2S removal from gas streams over γ-FeOOH, γ-Fe2O3 and α-Fe2O3: effects of hydroxyl group, defect and specific surface area
Ind. Eng. Chem. Res.
Boosting acetone oxidation efficiency over MnO2 nanorods by tailoring crystal phases
N. J. Chem.
Recent advances in manganese oxide nanocrystals: fabrication, characterization, and microstructure
Chem. Rev.
Long-term stability against H2S poisoning on Pd composite membranes by thin zeolite coatings
Ind. Eng. Chem. Res.
Investigation into the catalytic roles of various oxygen species over different crystal phases of MnO2 for C6H6 and HCHO oxidation
ACS Catal.
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