Activated carbon-supported catalyst loading of CH4N2O for selective reduction of NO from flue gas at low temperatures

• Published in: International journal of hydrogen energy 2019-05, Vol.44 (26), p.13523-13537
• Main Authors: Liu, Kaijie, Yu, Qingbo, Wang, Baolan, Xie, Huaqing, Duan, Wenjun, Qin, Qin
• Format: Article
• Language: English
• Subjects: Catalyst; Low temperature; Nitrogen oxides; Selective catalytic reduction; Transition metal oxide
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2019.03.253

Selective catalytic reduction of nitrogen oxides with loaded CH4N2O (low-temperature urea-SCR) is a novel and promising technology to remove nitrogen oxides from low-temperature oxygen-containing flue gas, which can avoid the problem of NH3 escape. In the present study, a series of industrial-grade biomass-based activated carbon (AC)-supported transition metal oxide catalysts with urea loading were prepared by ultrasound-assisted impregnation, and the physicochemical properties of the catalysts were observed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), graphite furnace atomic absorption spectroscopy (GFAAS), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) analysis, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The influences of the AC type, reaction temperature, AC particle size, metal oxide loading, urea load level and loaded active element type on the catalytic activity were studied through experiments. Moreover, the NO adsorption capacities of the AC carrier at different temperatures were also tested and calculated. The results of NO adsorption tests show that the adsorption capacity of AC decreased with increasing temperature. The results of the catalytic performance tests indicate that the copper- and manganese-based catalysts with 6 wt% urea exhibited better activity than the other catalysts. The copper-based catalyst, in particular, yielded better than 93% NO conversion at low temperatures (50–100 °C). Finally, on the basis of the combined characterization results and thermodynamics analysis, a NO removal mechanism of the copper- and manganese-based catalysts was proposed and discussed; the electron transfers of Mn4+ ⇌ Mn2+ and Cu2+ ⇌ Cu0 promoted the low-temperature urea-SCR method. •Hydroxyl and isonitrile CN groups are conducive to low-temperature urea-SCR.•NO oxidation is the rate-limiting and key step of low-temperature urea-SCR.•Nutshell-based activated carbon is suitable as carrier for low-temperature urea-SCR.•Copper and manganese have higher catalytic activity than other transition metals.•Electron transfers of Mn4+ ⇌ Mn2+ and Cu2+ ⇌ Cu0 promote low-temperature urea-SCR.