Simultaneous removal of CO2, NOx and SOx using single stage absorption column

Capturing flue gases often require multiple stages of scrubbing, increasing the capital and operating costs. So far, no attempt has been made to study the absorption characteristics of all the three gases (NO, SO₂ and CO₂) in a single stage absorption unit at alkaline pH conditions. We have attempted to capture all the three gases with a single wet scrubbing column. The absorption of all three gases with sodium carbonate solution promoted with oxidizers was investigated in a tall absorption column. The absorbance was found to be 100% for CO₂, 30% for NO and 95% for SO₂ respectively. The capture efficiency of sodium carbonate solution was increased by 40% for CO₂ loading, with the addition of oxidizer. Absorption kinetics and reaction pathways of all the three gases were discussed individually in detail.     

Improvement of the activity and SO2 tolerance of Sb-modified Mn/PG catalysts for NH3-SCR at a low temperature

A series of MnM/palygorskite (PG) (M = La, W, Mo, Sb, Mg) catalysts was prepared by the wetness co-impregnation method for low-temperature selective catalytic reduction (SCR) of NO with NH₃. Conversion efficiency followed the order Sb > Mo > La > W > Mg. A combination of various physico-chemical techniques was used to investigate the influence of Sb-modified Mn/PG catalysts. MnSb_0.156/PG catalyst showed highest NO conversion at low temperatures in the presence of SO₂ which reveals that addition of Sb oxides effectively enhances the SCR activity of catalysts. A SO₂ step-wise study showed that MnSb_0.156/PG catalyst displays higher durable resistance to SO₂ than Mn/PG catalyst, where the sulfating of active phase is greatly inhibited after Sb doping. Scanning electron microscopy and X-ray diffraction results showed that Sb loading enhances the dispersion of Mn oxides on the carrier surface. According to the results of characterization analyses, it is suggested that the main reason for the deactivation of Mn/PG is the formation of manganese sulfates which cause the permanent deactivation of Mn-based catalysts. For Sb-doped Mn/PG catalyst, SO_x ad-species formed were mainly combined with SbO_x rather than MnO_x. This preferential interaction between SbO_x and SO₂ effectively shields the MnO_x as active species from being sulfated by SO₂ resulting in the improvement of SO₂ tolerance on Sb-added catalyst. Multiple information support that, owing to the addition of Sb, original formed MnO_x crystallite has been completely transformed into highly dispersed amorphous phase accounting for higher SCR activity.     

Investigation of the common intermediates over Fe-ZSM-5 in NH3-SCR reaction at low temperature by in situ DRIFTS

The surface species formed in the reaction of NO and NO₂ with pre-adsorbed NH₃ over a FeZSM-5 catalyst(1.27 wt.% Fe, SiO₂/Al₂O₃ = 25) at low temperature(140 °C) were studied by in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS). Through using a background spectrum of NH 3-saturated Fe-ZSM-5, we clearly observed the formation of common intermediates resulting from the reaction of NO₂ or NO + O₂ w...     

Simultaneous oxidation of Mn(II) and As(III) on cupric oxide (CuO) promotes As(III) removal at circumneutral pH

Oxidation of Mn(II) or As(III) by molecular oxygen is slow at pH < 9, while they can be catalytically oxidized in the presence of oxide minerals and then removed from contaminated water. However, the reaction mechanisms on simultaneous oxidation of Mn(II) and As(III) on oxide mineral surface and their accompanied removal efficiency remain unclear. This study compared Mn(II) oxidation on four common metal oxides (γ-Al₂O₃, CuO, α-Fe₂O₃ and ZnO) and investigated the simultaneous oxidation and removal of Mn(II) and As(III) through batch experiments and spectroscopic analyses. Among the tested oxides, CuO and α-Fe₂O₃ possess greater catalytic activity toward Mn(II) oxidation. Oxidation and removal kinetics of Mn(II) and As(III) on CuO indicate that O₂ is the terminal electron acceptor for Mn(II) and As(III) oxidation on CuO, and Mn(II) acts as an electron shuttle to promote As(III) oxidation and removal. The main oxidized product of Mn(II) on CuO is high-valent MnO_x species. This newly formed Mn(III) or Mn(IV) phases promote As(III) oxidation on CuO at circumneutral pH 8 and is reduced to Mn(II), which may be then released into solution. This study provides new insights into metal oxide-catalyzed oxidation of pollutants Mn(II) and As(III) and suggests that CuO should be considered as an efficient material to remediate Mn(II) and As(III) contamination.     

Adsorption performance of CMK-3 and C-FDU-15 in NO removal at low temperature

CMK-3 and C-FDU-15 samples were synthesized using hard-templating and evaporationinduced self-assembly(EISA) methods,respectively.The pore structures of CMK-3 and CFDU-15 as well as commercial activated carbon were characterized by means of X-ray diffraction,field emission scanning electron microscopy,transmission electron microscopy,and N₂ adsorption–desorption.Adsorption of NO was investigated by means of thermogravimetric analysis,temperature-programmed desorption of NO + O₂     

Catalytic performance and reaction mechanisms of NO removal with NH3 at low and medium temperatures on Mn-W-Sb modified siderite catalysts

Iron-based catalysts have been explored for selective catalytic reduction (SCR) of NO due to environmentally benign characters and good SCR activity. Mn-W-Sb modified siderite catalysts were prepared by impregnation method based on siderite ore, and SCR performance of the catalysts was investigated. The catalysts were analyzed by X-ray diffraction, H₂-temperature-programmed reduction, Brunauer-Emmett-Teller, Thermogravimetry-derivative thermogravimetry and in-situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS). The modified siderite catalysts calcined at 450°C mainly consist of Fe₂O₃, and added Mn, W and Sb species are amorphous. 3Mn-5W-1.5Sb-siderite catalyst has a wide temperature window of 180-360°C and good N₂ selectivity at low temperatures. In-situ DRIFTS results show NH₄⁺, coordinated NH₃, NH₂, NO₃⁻ species (bidentate), NO₂⁻ species (nitro, nitro-nitrito, monodentate), and adsorbed NO₂ can be discovered on the surface of Mn-W-Sb modified siderite catalysts, and doping of Mn will enhance adsorbed NO₂ formation by synergistic catalysis with Fe³⁺. In addition, the addition of Sb can inhibit sulfates formation on the surface of the catalyst in the presence of SO₂ and H₂O. Time-dependent in-situ DRIFTS studies also indicate that both of Lewis and Brønsted acid sites play a role in SCR of NO by ammonia at low temperatures. The mechanism of NO removal on the 3Mn-5W-1.5Sb-siderite catalyst can be discovered as a combination of Eley-Rideal and Langmuir-Hinshelwood mechanisms with three reaction pathways. The mechanism of NO, oxidized by synergistic catalysis of Fe³⁺ and Mn^4+/3+ to form NO₂ among three pathways, reveals the reason of high NO_x conversion of the catalyst at medium and low temperatures.

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