Understand the role of redox property and NO adsorption over MnFeOx for NH3-SCR

Widening the operation temperature window of selective catalytic reduction NO by NH3 (NH3-SCR) is a challenge to meet the increasingly stringent emission control regulations of NOx. Hence, MnFeOx with different...

Oxidation of NO x Using Hydrogen Peroxide Vapor over Mo/TiO2

xMo/TiO₂ catalysts (x = 1, 2, 3, and 4%) were prepared using the coprecipitation method in the present study. The coprecipitation method was used in the thermal catalytic decomposition of H₂O₂ steam to treat NO _x at a low temperature range (80-160 °C). Several characterization techniques have been employed, such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller measurements, transmission electron microscopy (TEM), scanning electron microscopy and energy-dispersive X-ray spectrometry (SEM-EDXS), and Fourier transform infrared spectroscopy. The activity tests showed that the incorporation of molybdenum into TiO₂ led to a significant increase in the catalytic oxidation of NO, and under the condition of H₂O₂/NO = 6:1 (molar ratio), the NO _x removal rate of 2% Mo/TiO₂ is the highest, reaching 92.56%. XRD, TEM, and SEM-EDXS analyses showed that Mo was well dispersed on the surface of an anatase-phase TiO₂. XPS analysis indicated that Mo mixed with slag mainly existed in the form of Mo⁶⁺. Moreover, in comparison with the mostly reported SCO catalysts, used for the elimination of NO, the prepared Mo/TiO₂ catalyst showed excellent stability and sulfur resistance.

The enhancement of NH3-SCR performance for CeO2 catalyst by CO pretreatment

CO pretreatment was found to effectively improve the SCR performance of CeO₂, with over 90% at about 300 °C. The larger specific area and the decrease of CeO₂ crystallization indicated the modification of the surface structure after CO pretreatment. Abundant Ce³⁺ species and active oxygen, better reducibility, and the higher surface adsorption capacity were mainly responsible for its enhanced SCR performance. DRIFT analysis revealed the presumed coexistence of two reaction routes that the L-H mechanism was related to the reaction temperature, while the reaction rate of E-R route was almost directly proportional to the NO concentration at a certain temperature, based on the kinetic calculation. In addition, the CO-pretreated CeO₂ also exhibited a better poisoning tolerance for SO₂ and H₂O and excellent thermal stability and circularity. Graphical abstract The process of NH₃-SCR reaction over CeO₂-CO catalyst.

Manganese oxides with hierarchical structures derived from coordination polymers and their enhanced catalytic activity at low temperature for selective catalytic reduction of NOx

Hierarchical manganese oxides with enhanced catalytic performance have been successfully synthesized via simple thermal annealing of manganese coordination polymer precursors, which is a facile, cost-effective, and environmentally benign preparation method. The resultant manganese oxide particles formed hierarchical structures with a starfish-like morphology and exhibited enhanced low-temperature SCR performance below 200 °C without dopants or supporting materials. In addition, the morphology, chemical states, crystal structure and acidity of manganese oxide catalysts prepared at different calcination temperatures were investigated. It is elucidated that enhanced SCR catalytic performance was strongly dependent on the hierarchical morphology of the catalysts.

Efficiency of Phosphotungstic Acid Modified Mn-Based Catalysts to Promote Activity and N2 Formation for Selective Catalytic Reduction of NO with Ammonia

In this work, the modified Mn-based NH3-SCR (NH3 low-temperature selective catalytic reduction) catalysts with excellent NO conversion and N2 selectivity be designed. N2 yield was hardly more than 75 % over MnOx/TiO2 for NH3-SCR reaction, whereas the NH3-SCR performance has been significantly improved by using 50 wt.% HPW (H3PW12O40)-MnOx/TiO2. 100 % NO conversion and more than 95 % N2 yield was obtained in wide operating temperature window (150–400°C), suggesting that the addition of HPW could effectively improve the NO reduction conversion. After that, the catalysts were further characterized by XRD, H2-TPR, XPS and in situ DRIFT. DRIFT analysis implied that the introduction of HPW significantly improve the capacity of NH4 + species adsorbed on Brønsted acid sites accompanied with inhibiting the formation and consumption of nitrite species. It proved that the non-selective catalytic reduction reaction over HPW-MnOx/TiO2 catalysts are restrained. HPW could accelerate the formation and consumption of NH4 + species adsorbed on Brønsted acid sites with deactivation of nitrate species. In addition, NH3(ad) could be hardly oxidized to NH species and then reacted with nitrate species (L-H mechanism) and gaseous NO (E-R mechanism). More importantly, the oxidation of NH3 was also suppressed, which plays a dominate role to form N2O above 300°C. Besides, the deactivation of potassium poisoning on the SCR activity significantly weakened for modified samples compared to parent catalyst.

Insight into the synergism between MnO2 and acid sites over Mn-SiO2@TiO2 nano-cups for low-temperature selective catalytic reduction of NO with NH3

The rational synthesis of low-temperature catalysts with high catalytic activity and stability is highly desirable for the selective catalytic reduction of NO with NH3. Here we synthesized a Mn-SiO2/TiO2 nano-cup catalyst via the coating of the mesoporous TiO2 layers on SiO2 spheres and subsequent inlay of MnO2 nanoparticles in the narrow annulus. This catalyst exhibited superior catalytic SCR activities and stability for low-temperature selective catalytic reduction of NO with NH3, with NO conversion of ∼100%, N2 selectivity above 90% at a temperature ∼140 °C. The characterization results, such as BET, XRD, H2-TPR, O2/NH3-TPD and XPS, indicated that this nano-cup structure catalyst possesses high concentration and dispersion of Mn4+ active species, strong chemisorbed O- or O2 2- species and highly stable MnO X active components over the annular structures of the TiO2 shell and SiO2 sphere, and thus enhanced the low-temperature SCR performance.

High N2 selectivity in selective catalytic reduction of NO with NH3 over Mn/Ti–Zr catalysts

A series of Mn-based catalysts were prepared by a wet impregnation method for the selective catalytic reduction (SCR) of NO with NH₃. The Mn/Ti–Zr catalyst had more surface area, Lewis acid sites, and Mn⁴⁺ on its surface, and showed excellent activity and high N₂ selectivity in a wide temperature range. NH₃ and NO oxidation was investigated to gain insight into NO reduction and N₂O formation. The formation of N₂O was primarily dominated by the reaction of NO with NH₃ in the presence of O₂via the Eley–Rideal mechanism. An intimate synergistic effect existed between the Mn-based and the Ti–Zr support. It was demonstrated that the Ti–Zr support greatly promoted the catalytic performance of Mn-based catalysts.

The Ti–Zr support greatly promotes the catalytic performance of Mn-based catalysts.

In situ fabrication of porous MnCoxOy nanocubes on Ti mesh as high performance monolith de-NOx catalysts

Porous MnCo_xO_y nanocubes on Ti mesh as monolith catalysts present enhanced de-NO_x performance.