The enhancement of Zn resistance of Mn/TiO2 catalyst for NH3-SCR reaction by the modification with Al2(SO4)3

Technological solutions for NOx, SOx, and VOC abatement: recent breakthroughs and future directions

NOx, SOx, and carbonaceous volatile organic compounds (VOCs) are extremely harmful to the environment, and their concentrations must be within the limits prescribed by the region-specific pollution control boards. Thus, NOx, SOx, and VOC abatement is essential to safeguard the environment. Considering the importance of NOx, SOx, and VOC abatement, the discussion on selective catalytic reduction, oxidation, redox methods, and adsorption using noble metal and non-noble metal-based catalytic approaches were elaborated. This article covers different thermal treatment techniques, category of materials as catalysts, and its structure-property insights along with the advanced oxidation processes and adsorption. The defect engineered catalysts with lattice oxygen vacancies, bi- and tri-metallic noble metal catalysts and non-noble metal catalysts, modified metal organic frameworks, mixed-metal oxide supports, and their mechanisms have been thoroughly reviewed. The main hurdles and potential achievements in developing novel simultaneous NOx, SOx, and VOC removal technologies are critically discussed to envisage the future directions. This review highlights the removal of NOx, SOx, and VOC through material selection, properties, and mechanisms to further improve the existing abatement methods in an efficient way.

CO + NH3 coupling denitration at low temperatures over manganese/activated carbon catalysts

To explore the mechanism of low-temperature carbon monoxide and ammonia (CO + NH₃) coupling denitration of manganese/activated carbon (Mn/AC) catalysts, Mn/AC series catalysts were prepared using the impregnation method with AC activated by nitric acid as a precursor and manganese nitrate as a precursor. We characterized the surface morphology, pore structure, active component phase, functional group, and active component valence change law of the Mn/AC catalyst. The denitration rate order with different Mn loadings is 7Mn/AC > 9Mn/AC > 5Mn/AC. When the Mn loading was 7%, the catalyst's surface was smooth, with a good pore structure and uniform surface distribution of metal particles. These features increased the reacting gas's contact area, improving the denitration rate. The reason for this was oxygen chemisorption on the catalyst's surface. The Mn⁴⁺ and the number of oxygen-containing functional groups on the catalyst surface increase after Mn loading increases; this provides more active sites for denitration and promotes the reaction's conversion to fast selective catalytic reduction. The low-temperature CO + NH₃ coupling denitration of Mn/AC catalysts conforms to the Langmuir-Hinshelwood mechanism when the temperature is lower than 230 °C and the Eley-Rideal mechanism when the temperature is higher than 230 °C. The research results can provide new ideas for low-temperature flue gas denitration.

Heavy metal poisoning resistance of a Co-modified 3Mn10Fe/Ni low-temperature SCR deNOx catalyst

Heavy metals have a great influence on the deNO_x efficiency of catalysts. The 3Mn10Fe/Ni catalyst that used nickel foam (Ni) as the carrier, Mn and Fe as the active components, and Co as a trace auxiliary was prepared using an impregnation method. The catalysts poisoned by Pb or Zn and Co-modified catalysts with Pb or Zn poisoning were studied. The addition of Pb or Zn significantly decreases the deNO_x activity of the 3Mn10Fe/Ni catalyst due to the decrease in the content of high-valence metal elements such as Fe³⁺ and Mn⁴⁺, lattice oxygen concentration, reduction performance, acidity, and the number of acid sites. However, after Co modification, the deNO_x activity of the poisoned catalysts can be improved effectively because the strong interaction between Pb or Zn and lattice oxygen is weakened, and the contents of lattice oxygen, high valence metal elements, reduction ability, and the number of acid sites increase.

The poisoning mechanisms of different zinc species on a ceria-based NH3-SCR catalyst and the co-effects of zinc and gas-phase sulfur/chlorine species

Low-medium temperature NH₃-SCR technology has been applied for years in municipal solid wastes incineration (MSWI) to control the emissions of nitrogen oxides. Unlike coal-fired flue gases, the tail gas from MSWI contains high levels of heavy metals in fly ash, especially the zinc species, which may harm SCR catalysts. As such, in this paper, the deactivation mechanism of different zinc species (ZnO, ZnSO₄ and ZnCl₂) on the Sb-CeZr₂O_x catalysts and the co-effects of zinc species and gas-phase pollutants (including SO₂ and HCl) were investigated. The experimental results indicated that the deactivation rate of various poisoning zinc species was in the order of ZnCl₂ > ZnSO₄ > ZnO. Moreover, the interactions between zinc and antimony species would disrupt the structure of the Sb-Ce mixed oxides to decrease the redox ability, consequently suppressing the ammonia activation and NO adsorption. Furthermore, such damaging effects on catalyst structures would promote the formation of bulk-like sulfate species in the presence of SO₂, resulting in a decreased mobility of surface oxygen species, which significantly decrease the sulfur resistance. However, the presence of HCl did not show an evident co-effect on the Zn poisoned sample owing to the limited coverage of the chlorine deposition.

Significantly enhanced Pb resistance of a Co-modified Mn–Ce–Ox/TiO2 catalyst for low-temperature NH3-SCR of NOx

Co modification can significantly improve the performance for low-temperature NH₃-SCR of NO_x and the Pb resistance of the Mn–Ce–O_x/TiO₂ catalyst.

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.