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Rationally Design Porous MnOx-FeOx Nanoneedles for LowTemperature Selective Catalytic Reduction of NOx by NH3 Zhaoyang Fan, Jian-Wen Shi, Chen Gao, Ge Gao, Baorui Wang, and Chunming Niu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 03 May 2017 Downloaded from http://pubs.acs.org on May 4, 2017
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ACS Applied Materials & Interfaces
Rationally Design Porous MnOx-FeOx Nanoneedles for LowTemperature Selective Catalytic Reduction of NOx by NH3 Zhaoyang Fan, Jian-Wen Shi*, Chen Gao, Ge Gao, Baorui Wang, Chunming Niu Center of Nanomaterials for Renewable Energy, State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
ABSTRACT In this work, a novel porous nanoneedle-like MnOx-FeOx catalyst (MnOx-FeOx nanoneedles) was developed for the first time by rationally heat-treating metal-organic frameworks including MnFe-precursor synthesized by hydrothermal method. A counterpart catalyst (MnOx-FeOx nanoparticles) without porous nanoneedle structure was also prepared by a similar procedure for comparison. The two catalysts were systematically characterized by the SEM, TEM, XRD, TG, XPS, H2-TPR, NH3-TPD, In-situ DRIFT, etc., and their catalytic activities were evaluated by the selective catalytic reduction (SCR) of NOx by NH3. The results showed that the rationally designed MnOx-FeOx nanoneedles presented outstanding low-temperature NH3-SCR activity (100% NOx conversion in a wide temperature window from 120 to 240 °C), high selectivity to N2 (nearly 100% N2 selectivity from 60 to 240 °C), excellent water resistance and stability in comparison with the counterpart MnOx-FeOx nanoparticles. The reasons can be attributed not only to the unique porous nanoneedle structure but also to the uniform distribution of MnOx and FeOx. More importantly, the desired Mn4+/Mnn+ and Oα/(Oα+Oβ) ratios as well as rich redox sites and abundant strong acid sites on the surface of the porous MnOx-FeOx nanoneedles also contribute to these excellent performances. In-situ DRIFT suggested that the NH3-SCR of NO over MnOx-FeOx nanoneedles follows both E-R and L-H mechanisms.
KEYWORDS: SCR, low temperature, MOF, MnOx-FeOx, porous nanoneedle structure
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1. INTRODUCTION Nitrogen Oxides (NOx, x=1,2), as one of the most harmful air pollutants, are mainly generated from the stationary sources (power plants) and mobile sources (diesel vehicles), and they lead to the formation of photochemical smog, acid rain, ozone depletion and greenhouse effect.1-3 So far, the most effective de-NOx technology is selective catalytic reduction (SCR) by ammonia.4 However, the commercial V2O5-WO3 (MoO3)/TiO2 catalysts fail to achieve the increasing critical standards of the modern society, such as the narrow operation temperature window (300-400 °C) and the toxicity of vanadium pentoxide to the human health and the environment.5 In addition, the novel strategy to locate the SCR unit downstream of the desulfurizer and electrostatic precipitator (ESP) to avoid the deactivation of the catalysts and the reheating of the flue gas have also promoted the development of low-temperature (
