Elsevier

Catalysis Today

Volume 376, 15 September 2021, Pages 302-310
Catalysis Today

Enhancement of low-temperature NH3-SCR catalytic activity and H2O & SO2 resistance over commercial V2O5-MoO3/TiO2 catalyst by high shear-induced doping of expanded graphite

https://doi.org/10.1016/j.cattod.2020.04.051Get rights and content

Highlights

  • V2O5-MoO3/TiO2-expanded graphite was first prepared by high shear technique.

  • Doping EG by high shear method enhanced low-temperature NH3-SCR catalytic activity of V2O5-MoO3/TiO2.

  • Doping EG by high shear method improved H2O&SO2 resistance of V2O5-MoO3/TiO2 catalyst.

  • The VO2+ and adsorbed oxygen species could be improved by this method.

Abstract

In this paper, the preparation of V2O5-MoO3/TiO2-expanded graphite (EG) by different methods was investigated to enhance the H2O resistance in SCR reaction. The catalyst with doping of EG by high shear method showed the best SCR performance. BET, TEM, XPS, H2-TPR, NH3-TPD and FT-IR were used to analyze the physicochemical characteristics of the prepared catalysts. The results indicated that TiO2 particles were distributed uniformly with EG by high shear method, which enhanced the surface area, increased Brönsted and Lewis acid sites and raised the VO2+ and adsorbed oxygen species on the surface. It was found that even with the addition of H2O (20 %) and SO2 at low temperature, the catalyst doping of EG by high shear method maintained about 90 % NO conversion. In addition, in-situ DRIFT spectra results showed that the NH3-SCR reaction over Cat-1 and Cat-2 followed the E-R and L-H mechanism, and the NH3 and NOx adsorbed species on the surface of Cat-2 possessed higher activity in SCR reaction than Cat-1.

Introduction

Nitrogen oxides (NOx) are considered as one of the major atmospheric pollutants [1]. Selective catalytic reduction (SCR) is the main method for NOx removal due to its high performance among various deNOx technologies [2]. SCR catalyst is the core component of these technologies, where commercial catalysts such as V2O5-WO3(MoO3)/TiO2 have been extensively utilized for decades with reaction temperatures ranging between 300−400 °C [3]. However, in many industries, the temperature of flue gas is lower than 250 °C requiring commercial SCR catalysts to be reheated, resulting in additional energy consumption [4,5]. Therefore, researchers have focused on SCR catalysts with high deNOx activity at low temperature.

In recent years, many low-temperature SCR catalysts have been developed such as V2O5 [6,7], MnOx [[8], [9], [10]], and CeO2 based catalysts [11,12]. However, H2O and SO2 in flue gas exhibit significant inhibitory effect toward SCR reaction at low temperature. Numerous reports have shown that H2O inhibits SCR catalyst activity due to the competitive adsorption between H2O and NH3 on the active site of SCR catalysts. Furthermore, H2O influences hydroxyl formation on the surface, which decreases the adsorption capacity of NH3 [13,14]. To improve the resistance of H2O toward SCR catalyst at low temperature, focus has been on the addition hydrophobic material, such as polytetrafluoroethylene, carbon nanotubes, graphene, which are good supports with hydrophobic properties [[15], [16], [17]]. Zhang et al. [18] prepared Mn-Ce oxide in situ on carbon nanotubes, demonstrating that the method could strengthen the binging force of oxide and carbon nanotubes which enhances the resistance to SO2 and H2O due to the promotion of ammonium sulfate decomposition. Lu et al. [19] reported that TiO2-graphene nanocomposite could support the preparation of Ce-Mn based SCR catalysts, where the hydrophobic groups of graphene reduce the adsorption of H2O on the catalyst, producing excellent resistance to H2O and SO2. Thus, the addition of hydrophobic carbon-based materials enhances H2O resistance of SCR catalysts. However, such materials are not only expensive, but also difficult to combine with other supports through simple impregnation method due to their hydrophobic properties, which limits their industrial application. Moreover, most mechanical methods such as ball-milling destroy the structure of carbon materials [20]. Therefore, the development of low temperature SCR catalysts with excellent H2O and SO2 resistance suitable for practical application is still a challenge for researchers.

The high shear approach is an efficient dispersion technology in the field of material synthesis [21]. It is realized utilizing a high shear disperser emulsification machine, which is mainly composed of a fixed stator and rotating rotor. Due to the small gap between stator and rotor, high tangent speed and high frequency mechanical effect caused by high-speed rotation of the rotor can force immiscible materials to effectively and rapidly homogenized. In this paper, TiO2-expanded graphite (TiO2-EG) nanocomposite was prepared by high shear technology. Vanadium and molybdenum active component were loaded onto composites by impregnation. XRD, TEM, H2-TPR, NH3-TPD, and FT-IR techniques were used to characterize the physicochemical properties of the samples.

Section snippets

Catalyst preparation

TiO2-expanded graphite (TiO2-EG) nanocomposites with mass ratios of 10 wt.% EG were prepared by high shear-induced method. Frist, EG (Advanced Materials, China, 98 %) and anatase TiO2 (Xinhua, China, 99 %) was dissolved in deionized water by ultrasonic agitation treatment for 10 min. The slurry was placed into the colloid mill (XMD2000/4, made by Taicang SID Machinery Technology Co., Ltd) and treated for 3 h. Next, the slurry was dehydrated over night at 100 °C and then calcined at 500 °C for 5

Results and discussion

NH3-SCR performance of all samples is shown in Fig. 1. Fig. 1A shows that all samples display 100 % NO conversion at temperatures >200 °C and a significant different of NO conversions in the range of 140−200 °C. Obviously, Cat-2 exhibits the greatest SCR activity at low temperature, with 100 % NO conversion at 180 °C, whereas Cat-1 is only 81 % at the same temperature. This suggests that the doping of EG by high shear method improves the low temperature NH3-SCR performance. It has been reported

Conclusion

In this paper, the effect of doping of EG with different methods on SCR performance over V2O5-MoO3/TiO2 was investigated, with those prepared via the high shear method displaying excellent SCR performance. It was revealed by BET, TEM, XPS and H2-TPR analysis that TiO2 particles were distributed uniformly with EG by high shear method, which enhanced the surface area and increases VO2+ and adsorbed oxygen species on the surface. Meanwhile, NH3-TPD and FT-IR results suggested that the catalyst

Credit author statement

R. Wu, N. Zhang, and H. He conceived the idea and co-wrote the paper. R. Wu, L. Li performed most of the reactions, collected and analysed the data. J. He, L. Song and G. Zhang performed the part experiments and analysed the data. Z. Zhang discussed the results and commented on the manuscript.

Conflicts of interest

There are no conflicts of interest to declare.

Acknowledgment

This work was financially supported by the National Key R&D Program of China (2017YFC0210303) and Natural Science Foundation of China (21806005).

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    R. Wu and L.C. Li contributed equally to this work.

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