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Bulk Vanadium Oxide versus Conventional VO/TiO: NHSCR Catalysts Working at a Low Temperature Below 150C o
Yusuke Inomata, Shin-ichi Hata, Makoto Mino, Eiji Kiyonaga, Keiichiro Morita, Kenji Hikino, Kazuhiro Yoshida, Hiroe Kubota, Takashi Toyao, Ken-Ichi Shimizu, Masatake Haruta, and Toru Murayama ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b02695 • Publication Date (Web): 26 Aug 2019 Downloaded from pubs.acs.org on August 27, 2019
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ACS Catalysis
Bulk Vanadium Oxide versus Conventional V2O5/TiO2: NH3-SCR Catalysts Working at a Low Temperature Below 150oC Yusuke Inomata,‖ Shin-ichi Hata, ‖,┴ Makoto Mino,‖ Eiji Kiyonaga,† Keiichiro Morita,† Kenji Hikino,† Kazuhiro Yoshida,† Hiroe Kubota,‡ Takashi Toyao,‡ Ken-ich Shimizu,‡ Masatake Haruta,‖ and Toru Murayama‖,* ‖
Research Center for Gold Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University Hachioji, Tokyo 192-0397, Japan ┴ Department of Engineering, Sanyo-Onoda City University, Sanyo-Onoda, Yamaguchi 756-0884, Japan † Energia Economic and Technical Research Institute, the Chugoku Electric Power Company, Incorporated, HigashiHiroshima, Hiroshima 739-0046, Japan ‡ Institute for Catalysis, Hokkaido University, Sapporo, Hokkaido 001-0021, Japan ABSTRACT: Practical catalysts that work at a low temperature for selective catalytic reduction of NOx using NH3 (NH3-SCR) have been required to treat NOx at the outlet temperature in boiler systems (100-150oC). In this paper, we report bulk vanadium oxide catalysts that show NH3-SCR activity at a low temperature below 150oC. Defective bulk vanadium oxide (V(V)+V(IV)) catalysts were synthesized by the calcination of vanadium(IV) oxalates at 270oC (1-4 h). The reaction rate per mol of surface vanadium atom of the catalyst calcined at 270oC for 2 h (V 270-2, 6.4 ×10-2 molNO molV -1s-1) was 10-14 times faster than those of conventional 1-9 wt% V2O5/TiO2 (4.5 ×10-3–6.1 ×10-3 molNO molV -1s-1), indicating that bulk vanadium oxide is more favorable for NH3-SCR and V(IV) species enhance the activity. The NH3-SCR of V 270-2 is driven by Lewis acid mechanism, which proceeds faster than Brønsted acid mechanism.
KEYWORDS: vanadium oxide, NO, NH3-SCR, defect, heterogeneous catalyst A denitration process is an industrially important step for removing harmful NOx (NO and NO2) from exhaust gas emitted by the combustion of fossil fuels, coal and natural gas, which can become a cause of acid rain and photochemical smog. Selective catalytic reduction of NOx using NH3 (NH3-SCR) is generally used for the process to convert NOx into harmless N2 and water in facilities such as thermal power stations and waste treatment plants.1 4NO + 4NH3 + O2 → 4N2 + 6H2O 2NO2 + 4NH3 + O2 → 3N2 + 6H2O Among the various NH3-SCR catalysts, supported vanadium oxide catalysts and zeolite catalysts have been focused on for practical use.1–10 Supported vanadium (V) oxide catalysts, such as V2O5/TiO2 and V2O5-WO3/TiO2, have been used successfully in stationary applications.1–4 The V-based catalysts show higher N2 selectivity than other active metal oxides. V2O5WO3/TiO2 catalysts have been commercialized and utilized as industrial catalysts owing to the chemical stability of the titania support and low activity for SO2 oxidation. Small-pore copper-exchanged zeolites like Cu-SSZ-13 have recently attracted much attention, and the application of an NH3-SCR catalyst to automobiles has been considered because of its wide operating temperature window, thermal stability, and tolerance against the vibration of a moving automobile.8–10 However, the working temperatures of these catalysts are above 200oC. In the current boiler systems, for example, SCR catalysts are usually placed just below the boilers because the catalyst
needs high reaction temperature (>300oC) for low vanadium content (0.5–1.5 wt%),11,12 where the catalyst will be damaged physically by ash. Moreover, the undesired SO2 oxidation, causing the blockage of catalyst and deactivation by the formation of NH4HSO4 and (NH4)2SO4, increasingly proceeds with an increase in the loading amount of V2O5 at temperatures above 300oC.13 If SCR catalysts can work at lower reaction temperature and are placed downstream of the system, the next-generation stationary SCR system does not require additional reheating facilities and can avoid catalyst deactivation due to sulfates and ash. Although Mn, Cu, and Cr oxides have been shown to have the potential for use in lowtemperature NH3-SCR catalysts (
