Enhanced Oxygen Vacancies in a Two-Dimensional MnAl-Layered Double Oxide Prepared via Flash Nanoprecipitation Offers High Selective Catalytic Reduction of NOx with NH₃

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.

Manganese-based layered double hydroxide nanoparticles as highly efficient ozone decomposition catalysts with tunable valence state

Manganese oxides are well explored effective ozone decomposition catalysts, but the accumulation of oxygen trapped on their surfaces and high valence state restrict their catalyst efficiency. Herein, we report manganese based layered double hydroxide (LDH) catalysts with different average oxidation states (AOS) of Mn. MgMnAl-LDH catalysts show large specific surface area, abundant oxygen vacancies, stable structure and excellent catalytic ozone decomposition performance. The valence state of Mn can be tuned by adjusting the metallic element ratio in the LDH matrix, and a catalyst with AOS of only 2.3 is acquired. The impacts of the valence states of Mn on the catalytic ozone decomposition process were further studied by density functional theory (DFT) calculations. It is found that the Mn²⁺ facilitates the desorption of generated oxygen on the surface of LDHs, while Mn³⁺ and Mn⁴⁺ contribute to the dissociation of adsorbed ozone.

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.

In situ doping of M (M = Cu, Ni, Co) into MnAl-LDH laminate to promote the NH₃-SCR performance of the MnAl-LDO catalyst.

A Critical Review of Recent Progress and Perspective in Practical Denitration Application

Nitrogen oxides (NOx) represent one of the main sources of haze and pollution of the atmosphere as well as the causes of photochemical smog and acid rain. Furthermore, it poses a serious threat to human health. With the increasing emission of NOx, it is urgent to control NOx. According to the different mechanisms of NOx removal methods, this paper elaborated on the adsorption method represented by activated carbon adsorption, analyzed the oxidation method represented by Fenton oxidation, discussed the reduction method represented by selective catalytic reduction, and summarized the plasma method represented by plasma-modified catalyst to remove NOx. At the same time, the current research status and existing problems of different NOx removal technologies were revealed and the future development prospects were forecasted.

Layered Double Hydroxide-Based Nanomaterials-From Fundamentals to Applications

Layered double hydroxides (LDHs) and their composites with various substances represent an important class of materials suitable for several existing and future applications in biological, chemical, and environmental processes [...].

High CO Methanation Performance of Two-Dimensional Ni/MgAl Layered Double Oxide with Enhanced Oxygen Vacancies via Flash Nanoprecipitation

As a methanation tool, two-dimensional (2D) carrier-loaded Ni has attracted the attention of many researchers. We successfully prepared 2D MgAl layered double oxides (LDO) carriers via flash nanoprecipitation (FNP). Compared to the LDO samples prepared by conventional co-precipitation (CP), the 2D MgAl-LDO (FNP) has more oxygen vacancies and more exposed active sites. The Ni/MgAl-LDO (FNP) catalyst demonstrates a CO conversion of 97%, a CH4 selectivity of 79.8%, a turnover frequency of 0.141 s−1, and a CH4 yield of 77.4% at 350 °C. The weight hourly space velocity was 20,000 mL∙g−1∙h−1 with a synthesis gas flow rate of 65 mL∙min−1, and a pressure of 1 atm. A control experiment used the CP method to prepare Ni/MgAl-LDO. This material exhibits a CO conversion of 81.1%, a CH4 selectively of 75.1%, a TOF of 0.118 s−1, and a CH4 yield of 61% at 450 °C. We think that this FNP method can be used for the preparation of more 2D LDO catalysts.