Effect of iron loading on the performance and structure of Fe/ZSM-5 catalyst for the selective catalytic reduction of NO with NH3

Remarkable enhancement in the N2 selectivity of NH3-SCR over the CeNb3Fe0.3/TiO2 catalyst in the presence of chlorobenzene

The simultaneous removal of NO_x and dioxins is the frontier of environmental catalysis, which is still in the initial stage and poses several challenges. In this study, a series of CeNb₃Fe_x/TiO₂ (x = 0, 0.3, 0.6, and 1.0) catalysts were prepared by the sol-gel method and examined for the synergistic removal of NO_x and CB. The CeNb₃Fe_0.3/TiO₂ catalyst exhibits an optimum catalytic performance, with an NO_x conversion greater than 95% at 260-380 °C. It also exhibits an optimal CB oxidation activity, in which CB promoted both the NO_x conversion and N₂ selectivity below 250 °C. Moreover, the more favorable ratios of Ce⁴⁺ to Ce³⁺ and plentiful surface-adsorbed oxygen species are the reasons why CeNb₃Fe_0.3/TiO₂ catalyst has better catalytic activity than other catalysts at the lower temperature. Simultaneously, owing to the modulation of Fe to the redox properties of Ce and Nb, the large number of oxygen vacancies and acid sites was generated, and the CeNb₃Fe_0.3/TiO₂ catalyst is beneficial to NO_x reduction and CB oxidation. Furthermore, the results of in situ DRIFTS study reveal the NH₃-SCR reactions over CeNb₃Fe_0.3/TiO₂ catalysts are mainly conformed to by the L-H mechanism (< 350 °C) and E-R mechanism (> 350 °C), respectively, and the multi-pollutant conversion mechanism in the synergistic reaction was systematically studied.

The Study of C3H6 Impact on Selective Catalytic Reduction by Ammonia (NH3-SCR) Performance over Cu-SAPO-34 Catalysts

In present work, the catalytic performance of Cu-SAPO-34 catalysts with or without propylene during the NH3-SCR process was conducted, and it was found that the de-NOx activity decreased during low temperature ranges (<350 °C), but obviously improved within the range of high temperatures (>350 °C) in the presence of propylene. The XRD, BET, TG, NH3-TPD, NOx-TPD, in situ DRIFTS and gas-switch experiments were performed to explore the propylene effect on the structure and performance of Cu-SAPO-34 catalysts. The bulk characterization and TG results revealed that neither coke deposition nor the variation of structure and physical properties of catalysts were observed after C3H6 treatment. Generally speaking, at the low temperatures (<350 °C), active Cu2+ species could be occupied by propylene, which inhibited the adsorption and oxidation of NOx species, confining the SCR reaction rate and causing the deactivation of Cu-SAPO-34 catalysts. However, with the increase of reaction temperatures, the occupied Cu2+ sites would be recovered and sequentially participate into the NH3-SCR reaction. Additionally, C3H6-SCR reaction also showed the synergetic contribution to the improvement of NOx conversion at high temperature (>350 °C).

NO oxidation performance and kinetics analysis of BaMO3 (M=Mn, Co) perovskite catalysts

Perovskite is an efficient and emerging catalyst for NO oxidation. In this study, BaMnO₃ and BaCoO₃ perovskite catalysts were synthesized by the sol-gel method, and their catalytic oxidation performances of NO were studied. The catalytic performances indicated that BaMnO₃ and BaCoO₃ perovskites had the highest NO oxidation activities with the NO conversions of 78.2% at 350 °C and 84.3% at 310 °C, respectively. The high activities of BaMnO₃ and BaCoO₃ perovskite catalysts were related to the abundant surface adsorption oxygen (O_A = 76.21% and 78.57%, respectively) and the high concentration of Mn⁴⁺ (Mn⁴⁺/Mn = 66.95%) and Co³⁺ (Co³⁺/Co = 63.8%). Moreover, the results of FT-IR and kinetics revealed that NO and O₂ adsorbed on the surface of samples and combined with the B-O band to form bidentate nitrate and bridging nitrate, which eventually was converted into NO₂. The kinetics analysis revealed that the NO oxidation reaction followed the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. In addition, the activation energies were 36.453 kJ/mol for BaMnO₃ and 30.081 kJ/mol for BaCoO₃, implying that BaMnO₃ and BaCoO₃ provide low-cost and efficient catalysts, which can be comparable to Pt noble metal catalysts.

Adsorption mechanism of NH3, NO, and O2 molecules over the FexOy/AC catalyst surface: a DFT-D3 study

The surface model of the Fe_xO_y/AC catalyst was constructed and the adsorption mechanism of gas molecules on its surface was revealed.

Optimizing reaction conditions and experimental studies of selective catalytic reduction of NO by CO over supported SBA-15 catalyst

Selective catalytic reduction of NO with CO (CO-SCR) was investigated based on optimizing the operating conditions by response surface methodology (RSM) and by appropriately choosing the supported SBA-15 catalysts. The effects of the CO-SCR reaction parameters such as NO:CO molar ratios and oxygen concentrations on the catalytic performance were determined by RSM to evaluate the NO conversion using a first-order polynomial model. The CuO/SBA-15 and Fe₂O₃/SBA-15 catalysts were synthesized by a hydrothermal method and characterized by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), N₂ adsorption-desorption (BET), scanning electron microscopy coupled to energy dispersive X-Ray spectroscopy (SEM-EDS), and Fourier transform infrared spectroscopy (FTIR) to investigate the physicochemical properties of the solids. The RSM showed a very good agreement between predicted values and experimental results with the Pareto analysis confirming the accuracy and reliability of the model. The optimized results indicated the maximum NO conversion at 500 °C with using the NO to CO molar ratio of 1:2 (500:1000 ppm) in the absence of oxygen. Under these conditions, CuO/SBA-15 catalyst achieved 99.7% of NO conversion, whereas Fe₂O₃/SBA-15 had 98.1% of the catalytic parameter. Catalytic tests in CO-SCR reaction were performed on both catalysts at optimum operating conditions with CuO/SBA-15 exhibiting better performance compared to that of Fe₂O₃/SBA-15. The results revealed that CuO/SBA-15 was a promising catalyst for CO-SCR of NO due to the well-dispersed CuO phase on SBA-15 surface that allows the solid being more tolerant to the presence of oxygen.

The positive effect of siderite-derived α-Fe2O3 during coaling on the NO behavior in the presence of NH3

Siderite is a naturally occurring mineral that can be found extensively in coal. The structural evolution of siderite in the process of coaling and its performance in the transformation of NO in the presence of NH₃ were investigated in this work. In addition, the effects of the coexisting component, including vapor, SO₂, and the alkali metal K, were also discussed. Heat treatment was performed at 450, 500, 550, 600, and 700 °C to obtain siderite-derived α-Fe₂O₃, which was then evaluated in de-NO_x via the selective catalytic reduction (SCR) of NO with NH₃ in a fixed bed. The X-ray diffraction (XRD), the X-ray fluorescence spectrometer (XRF), N₂ adsorption-desorption (BET), the X-ray photoelectron spectrometer (XPS), the scanning electron microscope (SEM), and the transmission electron microscope (TEM) were used to investigate the variations in the morphology and structure of the thermally treated siderite. The results showed that siderite was gradually oxidized and decomposed into α-Fe₂O₃ with a nanoporous structure and large surface area of 27.27 m² g^-1 after calcination under an air atmosphere. The α-Fe₂O₃ derived from siderite at 500 °C (H500) exhibited an excellent SCR performance, where the NO conversion rate was great than 90% between 250 and 300 °C due to the pore structure and high specific surface area, additional adsorbed oxygen states, abundant oligomeric Fe oxide clusters, and large amount of acid sites. Regardless of the vapor content, SO₂ concentration, and reaction temperature, the α-Fe₂O₃ derived from siderite at 500 °C (H500) still favored the conversion of NO. When the reaction temperature was lower than 350 °C, H500 favored the conversion of NO even in the presence of an alkali metal (K). The experimental data demonstrated the positive effect of siderite-derived α-Fe₂O₃ in SCR technology and provided insight into NO behavior in coaling flue gas after NH₃ injection.