Synthesis of a Novel NiMnTi Mixed Metal Oxides from LDH Precursor and Its Catalytic Application for Selective Catalytic Reduction of NOx with NH3

Promotional effects of cerium and titanium on NiMn2O4 for selective catalytic reduction of NO by NH3

In this work NiMn2O4, NiMn2O4/TiO2 and NiMn2O4/CeO2 nanocomposites were prepared by co-precipitation method and evaluated for the selective catalytic reduction of NOx with NH3. Various characterization methods such as X-ray diffraction, field emission scanning electron microscope, specific surface area, average pore diameter, temperature programmed desorption (NH3-TPD), temperature-programmed reduction (H2-TPR) and inductively coupled plasma optical emission spectrometer were conducted to probe the physical and chemical properties of these catalysts. The catalytic activity tests showed that in the temperature window of 200–400 °C and the space velocity of 10,000–40,000 h−1, NiMn2O4/CeO2 demonstrated the best performance among the synthesized catalysts.

Layered double hydroxides and LDH-derived materials in chosen environmental applications: a review

With increasing global warming awareness, layered double hydroxides (LDHs), hydrotalcites, and their related materials are key components to reduce the environmental impact of human activities. Such materials can be synthesized quickly with high efficiency by using different synthesis processes. Moreover, their properties' tunability is appreciated in various industrial processes. Regarding physical and structural properties, such materials can be applied in environmental applications such as the adsorption of atmospheric and aqueous pollutants, hydrogen production, or the formation of 5-hydroxymethylfurfural (5-HMF). After the first part that was dedicated to the synthesis processes of hydrotalcites, the present review reports on specific environmental applications chosen as examples in various fields (green chemistry and depollution) that have gained increasing interest in the last decades, enlightening the links between structural properties, synthesis route, and application using lamellar materials.

Recent advances in layered double hydroxides (LDHs) derived catalysts for selective catalytic reduction of NOx with NH3

In recent years, layered double hydroxides (LDHs) derived metal oxides as highly efficient catalysts for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) have attracted great attention. The high dispersibility and interchangeability of cations within the brucite-like layers make LDHs an indispensable branch of catalytic materials. With the increasingly stringent and ultra-low emission regulations, there is an urgent need for highly efficient and stable low-medium temperature denitration catalysts in markets. In this contribution, we have critically summarized the recent research progress in the LDHs derived NH₃-SCR catalysts, including their ability for NO_x removal, N₂ selectivity, active temperature window, stability and resistance to poisoning. The advantages and defects of various types of LDHs-derived catalysts are comparatively summarized, and the corresponding modification strategies are discussed. In addition, considering the importance of the catalyst's resistance to poisoning in practical applications, we discuss the poisoning mechanism of each component in flue gases, and provide the corresponding strategies to improve the poisoning resistance of catalysts. Finally, from the perspective of practical applications and operation cost, the regeneration measures of catalysts after poisoning is also discussed. We hope that this work can give timely technical guidance and valuable insights for the applications of LDHs materials in the field of NO_x control.

Enhancement of NH3-SCR performance of LDH-based MMnAl (M = Cu, Ni, Co) oxide catalyst: influence of dopant M

Transition metal (Cu, Ni, Co) doped MnAl mixed oxide catalysts were prepared through a novel method involving the calcination of hydrotalcite precursors for the selective catalytic reduction of NO x with NH3 (NH3-SCR). The effects of transition metal modification were confirmed by means of XRD, BET, TEM, XPS, NH3-TPD, and H2-TPR measurements. Experimental results evidenced that CoMnAl-LDO presented the highest NO x removal efficiency of over 80% and a relatively high N2 selectivity of over 88% in a broad working temperature range (150-300 °C) among all the samples studied. Moreover, the CoMnAl-LDO sample possessed better stability and excellent resistance to H2O and SO2. The reasons for such results could be associated with the good dispersion of Co3O4 and MnO x , which could consequently provide optimum redox behavior, plentiful acid sites, and strong NO x adsorption ability. Furthermore, dynamics calculations verified the meaningful reduction in apparent activation energy (E a) for the CoMnAl-LDO sample, which is in agreement with the DeNO x activity.

Mesoporous MnOx-CeO2 composites for NH3-SCR: the effect of preparation methods and a third dopant

In this study, different preparation methods including an oxalate route, a nano-casting strategy and a traditional co-precipitation route were applied to obtain MnOx-CeO2 mixed oxides for selective catalytic reduction (SCR) of NO with NH3. The catalyst prepared from the oxalate route showed improved performance for NOx conversion and SO2 + H2O durability. To further improve the SO2 and H2O resistance of catalysts, ternary oxides were prepared from the oxalate route. The catalysts were studied by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), SO2 temperature-programmed desorption (SO2-TPD), and in situ diffuse reflectance infrared fourier transform spectroscopy (in situ DRIFTS). The nickel-manganese-cerium ternary oxide showed the best SO2 and H2O durability. The reason can be ascribed to its smaller pores, amorphous structure, and moderate amount of surface Mn3+/oxygen species, which could decrease chemical adsorption of SO2.

A Review of Low Temperature NH3-SCR for Removal of NOx

The importance of the low-temperature selective catalytic reduction (LT-SCR) of NOx by NH3 is increasing due to the recent severe pollution regulations being imposed around the world. Supported and mixed transition metal oxides have been widely investigated for LT-SCR technology. However, these catalytic materials have some drawbacks, especially in terms of catalyst poisoning by H2O or/and SO2. Hence, the development of catalysts for the LT-SCR process is still under active investigation throughout seeking better performance. Extensive research efforts have been made to develop new advanced materials for this technology. This article critically reviews the recent research progress on supported transition and mixed transition metal oxide catalysts for the LT-SCR reaction. The review covered the description of the influence of operating conditions and promoters on the LT-SCR performance. The reaction mechanism, reaction intermediates, and active sites are also discussed in detail using isotopic labelling and in situ FT-IR studies.