Improved Alkali-Tolerance of FeOx-WO3 Catalyst for NO Removal via in situ Reserving FeOx Active Species

In situ DRIFTS FT-IR and DFT study on Fe-V-W/Ti removal of NOx and VOCs

A series of indium-modified manganese oxide catalysts with different ratios were prepared by the homogeneous precipitation method. The appropriate amount of indium modification has many effects on the MnOx catalysts, such as increasing the specific surface area, increasing the concentration of surfactant Mn4+ and surface oxygen, enhancing the surface acid site strength, and improving the low-temperature activity of the MnOx catalysts. the Mn-InO-6 catalyst (Mn: In = 6:1) showed the best activity, maintaining approximately 100% NOx at conversion rates of 75–200 °C. Indium doping significantly improved the sulfur resistance of the MnOx catalyst with high reversibility and good stability. In situ DRIFTs indicate that the NH3-SCR reaction over Mn-InO-6 catalysts follows the Eley-Rideal and Langmuir-Hinshelwood mechanisms. 

Indium modified MnOx for high-efficient NH3-SCR De-NOx: Promotional role of indium and its catalytic performance

Direct decomposition of NO into N2 and O2 is an ideal technology for NOx removal. Catalyst deactivation by sulfur poisoning is the major obstacle for practical application. This paper focuses on strengthening the SO2 resistance of metal-exchanged HZSM-5 catalysts, by investigating the metals, promoters, preparation methods, metal-to-promoter molar ratios, Si/Al ratios and metal loadings. The results show that in the presence of SO2 (500 ppm), Fe is the best compared with Co, Ni and Cu. Cs, Ba and K modification enhanced the low-temperature activity of the Fe-HZSM-5 catalyst for NO decomposition, which can be further improved by increasing the exchanged-solution concentration and Fe/Cs molar ratio or decreasing the Si/Al molar ratio. Interestingly, Cs-doped Fe-HZSM-5 exhibited a high NO conversion and low NO2 selectivity but a high SO2 conversion within 10 h of continuous operation. This indicates that Cs-Fe-HZSM-5 has a relatively high SO2 resistance. Combining the characterization results, including N2 physisorption, XRD, ICP, XRF, UV–Vis, XPS, NO/SO2-TPD, H2-TPR and HAADF-STEM, SO42− was found to be the major sulfur species deposited on the catalyst’s surface. Cs doping inhibited the SO2 adsorption on Fe-HZSM-5, enhanced the Fe dispersion and increased the isolated Fe and Fe-O-Fe species. These findings could be the primary reasons for the high activity and SO2 resistance of Cs-Fe-HZSM-5.

https://www.mdpi.com/2073-4344/12/12/1579/pdf?version=1670232568

Enhanced SO2 Resistance of Cs-Modified Fe-HZSM-5 for NO Decomposition

Improvement of Sb-Modified Mn-Ce/TiO2 Catalyst for SO2 and H2O Resistance at Low-Temperature SCR

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 Bronsted 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 Mn4+/3+ to form NO2 among three pathways, reveals the reason of high NOx conversion of the catalyst at medium and low temperatures. Download : Download high-res image (64KB) Download : Download full-size image

Yuliang Wei

Papers

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