Promotional effects of Nb on selective catalytic reduction of NO with NH3 over Fe -Nb0.5--Ce0.5 (x = 0.45, 0.4, 0.35) oxides catalysts

Knowledge-Driven Experimental Discovery of Ce-Based Metal Oxide Composites for Selective Catalytic Reduction of NOx with NH3 through Interpretable Machine Learning

Mining the scientific literature, combined with data-driven methods, may assist in the identification of optimized catalysts. In this paper, we employed interpretable machine learning to discover ternary metal oxides capable of selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR). Specifically, we devised a machine learning framework utilizing extreme gradient boosting (XGB), identified for its optimal performance, and SHapley Additive exPlanations (SHAP) to evaluate a curated database of 5654 distinct metal oxide composite catalytic systems containing cerium (Ce) element, with records of catalyst composition and preparation and reaction conditions. By virtual screening, this framework precisely pinpointed a CeO2-MoO3-Fe2O3 catalyst with superior NOx conversion, N2 selectivity, and resistance to H2O and SO2, as confirmed by empirical evaluations. Subsequent characterization affirmed its favorable structural, chemical bulk properties and reaction mechanism. Demonstrating the efficacy of combining knowledge-driven techniques with experimental validation and analysis, our strategy charts a course for analogous catalyst discoveries.

Insights into Nb doping effects on the catalytic activity and SO2 tolerance of Mn-Cu/BCN catalyst for low-temperature NH3-SCR reaction

Biochar-based supported denitration catalysts have shown tremendous potential in reducing NOx, while improving low-temperature NH3-SCR catalytic activity and SO2 tolerance still faces great challenges. In this work, Mn7-Cu3/BCN and Mn7-Cu3-Nbx/BCN catalysts were prepared by one-step wet impregnation. The enhanced effect of Nb doping on the catalytic performance and SO2 tolerance over the Mn7-Cu3/BCN catalyst was evaluated in the temperature range of 75-275 °C. The denitrification activity test showed that the introduction of an appropriate amount of Nb increased the catalytic activity and N2 selectivity of the catalyst. The NO conversion of Mn7-Cu3-Nb0.05/BCN with an optimum doping ratio of 0.05 wt% Nb was higher than 94% at 150-275 °C. The characterization results indicated that the introduction of Nb enhanced the interaction between the active components MnOx and CuOx, accelerated the electron transfer between elements, and thus improved the Mn4+/Mnn+ and Oα/(Oα+Oβ+Oγ) proportions and redox performance. On the other hand, Nb modification increased the number of weakly acidic sites, which was beneficial for the adsorption and activation of the reducing agent NH3 under low-temperature conditions. Meanwhile, Nb could significantly improve the SO2 poisoning resistance of the Mn7-Cu3/BCN-S catalyst when SO2 was added to the reaction system. The NO conversion of Mn7-Cu3-Nb0.05/BCN remained above 75% after a 13.5 h reaction under 100 ppm SO2 and 5 vol% H2O at 225 °C. By combining experimental characterization results with DFT calculation results, we effectively confirmed that Mn7-Cu3-Nb0.05/BCN had good sulfur resistance, mainly because Nb could effectively inhibit the formation of manganese sulfate and promote the decomposition of ammonium bisulfate.

Promotional effects of Nb5+ and Fe3+ co-doping on catalytic performance and SO2 resistance of MnOx-CeO2 low-temperature denitration catalyst

As we know, SO₂ can cause MnO_x-CeO₂ (MnCeO_x) catalyst poisoning, which seriously shortens the service life of the catalyst. Therefore, to enhance the catalytic activity and SO₂ tolerance of MnCeO_x catalyst, we modified it by Nb⁵⁺ and Fe³⁺ co-doping. And the physical and chemical properties were characterized. These results illustrate that the Nb⁵⁺ and Fe³⁺ co-doping can optimally improve the denitration activity and N₂ selectivity of MnCeO_x catalyst at low temperature by improving its surface acidity, surface adsorbed oxygen as well as electronic interaction. What's more, NbO_x-FeO_x-MnO_x-CeO₂ (NbFeMnCeO_x) catalyst possesses an excellent SO₂ resistance due to less SO₂ being adsorbed and the ammonium bisulfate (ABS) formed on its surface tends to decompose, as well as fewer sulfate species formed on its surface. Finally, the possible mechanism that Nb⁵⁺ and Fe³⁺ co-doping enhances the SO₂ poisoning resistance of MnCeO_x catalyst is proposed.

Fabrication of BiFeO3-g-C3N4-WO3 Z-scheme heterojunction as highly efficient visible-light photocatalyst for water reduction and 2,4-dichlorophenol degradation: Insight mechanism

In this work, a Z-scheme BiFeO₃-g-C₃N₄-WO₃ (BFO-CN-WO) photocatalyst has been synthesized via a wet chemical method and utilized in photocatalysis for hydrogen generation and 2,4-dichlorophenol (2,4-DCP) degradation under visible light irradiation. The resultant photocatalyst showed 90 μmol·h^-1 g^-1 H₂ evolution activity and 63% 2,4-DCP degradation performance, which is 12 and 4.2 times higher than the pristine g-C₃N₄ respectively. The fascinating photocatalytic performance is attributed to the strong interfacial contact between g-C₃N₄ and the coupled BiFeO₃ and WO₃ component, which greatly improved the visible light absorption and charge carriers' separation. The designed Z-scheme heterojunction is a successful strategy for enhancing the separation efficiency of photo-induced charge carriers at the interface while retaining outstanding redox ability. During 2,4-DCP degradation, LC/MS technique was used to detect the reaction intermediates. According to the LC/MS results, several new intermediates such as 2,3-dichloro-6-(2,4-dichlorophenoxy)phenol (m/z = 306), 2,4-dichlorophenyl hydrogen carbonate (m/z = 207), 2,4-dichlorobenzen-1,3-diol (m/z = 177) and phenyl hydrogen carbonate (m/z = 137) were detected. Based on these intermediates, 2,4-DCP degradation pathway is proposed. The fluorescence (FL) and electron paramagnetic resonance (EPR) results reveal that the •OH plays an important role in the 2,4-DCP degradation. The fabricated photocatalyst can be utilized in the field of photocatalysis for practical applications.

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.