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Fe-Ce mixed oxides supported on carbon nanotubes for simultaneous removal of NO and Hg0 in flue gas Yaguang Ma, Dingyuan Zhang, Huamin Sun, Jiafeng Wu, Peng Liang, and Huawei Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00015 • Publication Date (Web): 21 Feb 2018 Downloaded from http://pubs.acs.org on February 21, 2018
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Industrial & Engineering Chemistry Research
Fe-Ce mixed oxides supported on carbon nanotubes for simultaneous removal of NO and Hg0 in flue gas
Yaguang Ma, Dingyuan Zhang, Huamin Sun, Jiafeng Wu, Peng Liang, Huawei Zhang*
College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266590 PR China
*Corresponding author. Tel.: +86-532-86057790
E-mail addresses:
[email protected] 1
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ABSTRACT: Developing simultaneous removal technology of NOx and Hg0 in flue gas is highly desirable but remains challenging. Multi-walled carbon nanotubes supported Fe-Ce mixed oxides nanoparticles (Fe(2)Ce(0.5)Ox/MWCNTs) were prepared using ethanol impregnation method for DeNOx and Hg0 removal. The NO and Hg0 removal efficiencies over catalyst reached to 99.1% and 88.9% at 240 °C and a space velocity of 30000 h-1. The Fe-Ce mixed oxides supported both inside and outside of MWCNTs in highly dispersed form with particle size of 3-5 nm. The Ce4+ existed on MWCNTs in two forms, some of which are the fluorite-like crystal CeO2, the other portion of Ce4+ entered the spinel structure of γ-Fe2O3 and led to the distortion of γ-Fe2O3lattice.Furthermore, it is evident that the chemisorbed oxygen content and oxidation activity of catalysts increased dramatically after Ce doping, which could be attributed to the excellent NH3-SCR and Hg0 removal performance.
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1. INTRODUCTION NO and Hg0 are the typical pollutants in flue gas which have adverse and harmful effects on environmental and human health. Many studies have been carried out to eliminate NO and Hg0emission.1-4Selective catalytic reduction (SCR) of NO with NH3 is one of the most effective cleaning technologies for stationary source, the commercial V-based catalysts have the disadvantages of narrow operation temperature window, toxicity of VOx and deactivation by high concentrationsof SO2 and dust.5-7 Therefore, it is extremely desirable to develop low-temperature 3
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SCR process and catalysts.He et al.8discussed the structure-activity relationship of Fe-, Ce-based oxide catalysts and Fe-, Cu-based zeolite catalysts in NH3-SCR reaction in detail, and proposed the surface modification of CeO2 or other metal oxides could be a promising way to prepare applicable catalysts. They also comprehensively reviewed recent studies on ceria for NH3-SCR catalysts when used as support, promoter, or the main active component.9 Shan et al.10,11 prepared A superior Ce-W-Ti mixed oxide catalyst by a facile homogeneous precipitation method and showed excellent NH3-SCR activity and 100% N2 selectivity with broad operation temperature window and extremely high resistance to space velocity, the excellent catalytic performance is associated with the highly dispersed active Ce and promotive W species on TiO2. Wang et al.12prepared Fe-Mn/Al2O3 catalyst for low temperature selective catalytic reduction (SCR) of NO with NH3. It was found that the Fe3+ was the main iron valence state on the catalyst surface and the addition of Mn increased the accumulation of Fe on the surface, and the 8Fe-8Mn/Al2O3 catalyst gave 99% of NO conversion at 150 °C. You et al.13 loaded different molar ratios of Mn/Ce on the on graphene for low-temperature SCR of NOx with NH3, the results indicated that these catalysts exhibited excellent low-temperature SCR activities and strong resistance against SO2. Boningari et al.14prepared Mn-Ce/TiO2 catalyst by adopting incipient wetness technique for the low-temperature selective catalytic reduction (SCR) of NOx with NH3 at industrial relevant conditions. The activity results showed that 93.0% NOx conversion was obtained over Mn-Ce(5.1)/TiO2-Hk at 100 °C and a space velocity of 80000 h-1. Multi-walled carbon nanotubes (MWCNTs) are formed by coiling of graphite sheets and have been reported to be a promising candidate of catalyst supports based on their excellent electron transport capacity, accessible surface and mechanical characteristics. Recently, MWCNTs have been interest as support for SCR process. Li et al.15optimized the V2O5/TiO2 catalyst and doped MWCNTs in it by sol-gel method, the denitration efficiency increased by 20% at 300°C.Huang et al.16 reported a V2O5/MWCNTs catalyst and the vanadium particles were highly dispersed on the surface of carbon nanotubes with particle size of 6-12 nm, its DeNOx efficiency reached more than 90% at 250 °C.Qu et al.17loaded 4
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nano-Fe2O3 on MWCNTs by ethanol impregnation method, the NOx conversion rate reached to 90% at 200-325 °C, and the catalyst exhibited excellent durability and stability for H2O and SO2. For the Hg0 removal from flue gas, many adsorbents such as activated carbons, zeolites, and metallic oxides have been widely researched. Catalytic oxidation is an effective method for Hg0 removal, in which Hg0 can be oxidized to Hg2+ and subsequently captured on the adsorbent surfaces. The most frequently used oxygen provider for catalytic oxidation included V2O5, MnOx, Fe2O3, CeO2 and so on, some of which are also widely used in SCR process.18-22Therefore, many researches focused on the synergistic removal of NO and Hg0 in flue gas using high-temperature SCR catalyst. To date, there is only a limited studying about low-temperature SCR and synergistic removal of Hg0 in flue gas. The temperature windows of low-temperature SCR are close to the operation temperature of Hg0 removal in flue gas (150-300°C), which made it is feasible for the simultaneous removal of NO and Hg0. The greatest challenge is developing high activity catalyst for NO catalytic reduction and Hg0 oxidation at low temperature. In this paper, Multi-walled carbon nanotubes supported Fe2O3 (Fe(2)/MWCNTs) and Fe-Ce mixed oxides nanoparticles (Fe(2)Ce(0.5)Ox/MWCNTs)were prepared using impregnation method in ethanol solution, and their catalytic performance for NO reduction with NH3 at low temperature (
