Elsevier

Chemosphere

Volume 287, Part 3, January 2022, 132336
Chemosphere

Photo- and thermo-catalytic mechanisms for elemental mercury removal by Ce doped commercial selective catalytic reduction catalyst (V2O5/TiO2)

https://doi.org/10.1016/j.chemosphere.2021.132336Get rights and content

Highlights

  • Ce doped V2O5/TiO2 displayed excellent thermo- and photo-catalytic properties.

  • Ce4+ had good oxidation performance and oxygen storage performance in Hg0 capture.

  • Ce doped V2O5/TiO2 presented good resistance to NO and SO2。.

  • DFT calculations for Hg0 adsorption were performed.

Abstract

The elemental mercury was catalytically removed by V2O5/TiO2 and Ce doped V2O5/TiO2 catalysts under the UV irradiation at 30–160 °C to determine whether the catalysts could simultaneously have both thermo- and photo-catalytic activities. The physicochemical properties of catalysts were characterized by XRD, SEM, EDX, BET, XPS, UV–visible, PER and EIS. The experimental results demonstrated that V2O5/TiO2 and Ce-doped catalysts possessed both thermo- and photo-catalytic reactivities. A suitable reaction temperature (120 °C) and UV light had promoting effects on mercury removal efficiency. In addition, owing to the high oxidation capability as well good oxygen storage performance of Ce4+, Ce doping could greatly improve the mercury removal properties of the catalyst, reduce the inhibition of SO2 and make NO the component with enhanced effect. Ce doping also had the capability of enhancing the light absorption intensity in the UV region as well as the separation rate of photoinduced carriers. Finally, DFT calculations of V-Ti and Ce-V-Ti for Hg0 removal were investigated to further verify the experimental conclusion.

Introduction

Mercury is widely regarded as a global pollutant that poses a serious threat to the human environment. The combustion of coal is one of the main causes of atmospheric mercury pollution in China (Pirrone et al., 2010). There are three main forms of mercury in coal-fired fiue gas mainly: oxidized mercury (Hg2+), particulate mercury (HgP) and elemental mercury (Hg0). Hg0 is particularly more difficult to control by existing contaminant removal devices than Hg2+ and HgP because of its inertness, high volatility and low solubility in water (Zhang et al., 2018; Mei et al., 2020). Hence, gaseous elemental mercury capture from coal-fired flue gas has been a great challenge to in the field of environmental pollution prevention and control. According to the existing experimental research, the most cost-effective commercial SCR catalysts (V2O5/TiO2) not only have remarkable NOx reduction performance, but also have the capability of promoting Hg0 oxidation at low temperature (Li et al., 2020a, 2021a, 2021b; Meng et al., 2019). Therefore, using commercial SCR catalyst for synergistic catalytic removal of elemental mercury is a promising and practical method. However, the integrated removal of NOx and mercury has been mainly based on the principle of thermal catalysis.

Up to date, photocatalytic oxidation technology has been deemed to have a wide application prospects for pollutant control and for energy utilization (Li et al., 2021c; Zhang et al., 2021; Cheng et al., 2019). Photocatalytic oxidants, with the advantages of strong oxidation and no secondary pollution, have the capability of removing elemental mercury more efficiently and environmentally. The photocatalytic behavior is largely dependent on the type of photocatalyst. TiO2 based photocatalysts are widely used in the field of photocatalysis because of its low preparation cost, good photostability and nontoxicity (Wang et al., 2020; Chen et al., 2020a; Li et al., 2021d). Therefore, Ti based catalysts were expected to be low-cost, environmentally friendly, and regenerable sorbents for simultaneous thermal and photocatalytic mercury removal in this paper. In recent years, the modification of TiO2 by cerium (Xu et al., 2002) and its oxides (Lin and Jimmy, 1998) to improve the photocatalytic performance have been reported in removing various environmental pollutants. CeO2 was judged to be a suitable choice for modifying TiO2 owing to its narrow band gap and Ce4+/Ce3+ reversible redox couple (Xie et al., 2021; Li et al., 2020b; Wang et al., 2013). The research showed that the reversible conversion between Ce(IV) and Ce(III) could realize efficient electron transfer between CeO2 and TiO2 (Yu et al., 2010), so as to improve the photocatalytic capability.

Few studies have revealed the effect of Ce on the thermo- and photo-oxidation performance of Hg0 on SCR catalysts through the combination of experiments and calculations. In this study, the Ce-doped V2O5/TiO2 catalysts were synthesized by the impregnation method and their catalytic properties were tested under the UV irradiation at 30–160 °C. In addition, density functional theory (DFT) calculations can be combined with the traditional experimental and characterization methods to better analyze the catalytic mechanism of elemental mercury.

Section snippets

Catalyst preparation

In this study, a V2O5/TiO2 catalyst (hereafter referred to as V-Ti) was used as the base catalyst, and Ce-modified catalysts were prepared by the impregnation method. First, V-Ti catalyst powder was stirred in 30 mL deionized water for 1 h. Then, the modified catalysts (0.4 % Ce, 0.8 % Ce, 1.2 % Ce, 1.6 % Ce and 2.0 % Ce) were prepared by Ce(NO3)3·6H2O solution. The V-Ti samples were filtered and dried for 24 h and calcined at different temperatures (400, 500 and 600 °C) for 2 h. Ce doped

BET analysis

The specific results are shown in Table S1. The larger the BET specific surface area is, the stronger the physical adsorption capacity is (Meng et al., 2019). The specific surface areas of V-Ti and Ce-V-Ti were 25.6–60.6, and 59.7–63.5 m2/g, respectively, and the pore volumes were 0.18–0.23 and 0.23–0.24 cm3/g, respectively, suggesting that there was a marked drop in the specific surface area of V-Ti according to increasing calcination temperatures from 400 to 600 °C, which was confirmed by the

Conclusion

V2O5/TiO2 catalysts were modified by cerium (Ce) through impregnation method. The mechanisms of Hg0 catalytic reaction were explained based on catalyst characterization. The catalysts displayed the highest mercury removal efficiency under UV light at 120 °C, revealing both of the photo-catalytic and thermo-catalytic mechanisms of Hg0 removal over V-Ti and Ce-V-Ti samples. The addition of Ce played a greatly promoting role in the mercury removal capability of the catalyst, resulting from that Ce

Credit author statement

Yili Zhang constructed the overall idea and innovation of the article. Yili Zhang did DFT related calculations and carried out the experiment. Jing Liu helped analyze calculation parts. Rihong xiao and Tian Gao helped experiment parts. Pengfei Liu and Bengen Gong helped with partial characterization analysis. Yili Zhang, Yongchun Zhao, Zhuo xiong and Junying zhang co-write the paper. Yongchun Zhao and Junying Zhang proposed and supervised the project. All authors revised 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

This work was supported by the National Key R&D Program of China (2019YFC1907000), the Program for HUST Academic Frontier Youth Team (2018QYTD05), the Key Research and Development Program of Hubei Province (2020BCA076) and the National Nature Science Foundation of China (NSFC) (42030807 and 51806076).

References (40)

  • Z. Shayegan et al.

    Surface fluorinated Ce-doped TiO2 nanostructure photocatalyst: a trap and remove strategy to enhance the VOC removal from indoor air environment

    Chem. Eng. J.

    (2020)
  • R. Stolle et al.

    Oxidation and reduction of mercury by SCR DeNOx catalysts under flue gas conditions in coal fired power plants

    Appl. Catal., B

    (2014)
  • Y. Wang et al.

    Ordered mesoporous CeO2-TiO2 composites: highly efficient photocatalysts for the reduction of CO2 with H2O under simulated solar irradiation

    Appl. Catal., B

    (2013)
  • B. Wang et al.

    A comparative study about the influence of metal ions (Ce, La and V) doping on the solar-light-induced photodegradation toward rhodamine B

    J. Environ. Chem. Eng.

    (2015)
  • L. Wang et al.

    Electrospun cerium-based TiO2 nanofibers for photocatalytic oxidation of elemental mercury in coal combustion flue gas

    Chemosphere

    (2017)
  • T. Wang et al.

    Photocatalytic removal of elemental mercury on TiO2-BiOIO3 heterostructures: mercury transformation,sulfur tolerance and SO2/SO3 conversion

    Chem. Eng. J.

    (2020)
  • L. Xie et al.

    A novel CeO2-TiO2/PANI/NiFe2O4 magnetic photocatalyst: preparation, characterization and photodegradation of tetracycline hydrochloride under visible light

    J. J. Solid. State. Chem.

    (2021)
  • A.-W. Xu et al.

    The Preparation, Characterization, and their photocatalytic activities of rare-earth-doped TiO2 Nanoparticles

    J. Catal.

    (2002)
  • Z. Yang et al.

    Promotional effect of CuO loading on the catalytic activity and SO2 resistance of MnOx/TiO2 catalyst for simultaneous NO reduction and Hg0 oxidation

    Fuel

    (2018)
  • Y. Yang et al.

    New insight into simultaneous removal of NO and Hg0 on CeO2-modified V2O5/TiO2 catalyst: a new modification strategy

    Fuel

    (2019)
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