Selective catalytic reduction of NOx with NH3 over a novel Co-Ce-Ti catalyst

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.

Unveiling alkali metal poisoning of CrMn catalyst for selective catalytic reduction of NOx with NH3: An experimental and theoretical study

Alkali metal poisoning has been an intricate and unsolved issue confining the catalytic activity of NH₃-SCR catalysts up to now. Herein, the effect of NaCl and KCl on catalytic activity of CrMn catalyst for NH₃-SCR of NO_x was systematically investigated to clarify the alkali metal poisoning by combined experiments and theoretical calculations. It unveiled that NaCl/KCl could deactivate CrMn catalyst due to the decrease in specific surface area, electron transfer (Cr⁵⁺+Mn³⁺↔Cr³⁺+Mn⁴⁺), redox ability and oxygen vacancy and NH₃/NO adsorption. In addition, NaCl cut off E-R mechanism reactions by inactivating surface Brønsted/Lewis acid sites. DFT calculations revealed that (1) Na and K could weaken MnO bond, (2) competitive adsorption between Cl and NH₃ was a main reason weakening Lewis acid, (3) Cl adsorption was also a major cause diminishing Brønsted acid and oxygen vacancy, (4) Both Na and K seriously impeded NO adsorption/activation, (5) NaCl/KCl increased the reaction heat of H₂O desorption (rate-determining step) in E-R mechanism reactions and KCl elevated its energy barrier in L-H mechanism reactions. Thus, this study provides the deep understanding of alkali metal poisoning and a well strategy to synthesize NH₃-SCR catalysts with outstanding alkali metal resistance.

Engineering yolk-shell MnFe@CeOx@TiOx nanocages as a highly efficient catalyst for selective catalytic reduction of NO with NH3 at low temperatures

To broaden the reaction temperature range and improve the H₂O-resistance of manganese-based catalysts, yolk-shell structured MnFe@CeO_x@TiO_x nanocages were prepared. The CeO₂ shell could effectively increase the oxygen vacancy defect sites, and the TiO₂ shell could remarkably improve the surface acid sites. Combining the advantages of the two shells could effectively solve the above questions. The catalytic efficiency of the yolk-shell MnFe@CeO_x@TiO_x-40 nanocages could reach above 90% in the range of 120-240 °C, and the water resistance could reach 90% at 240 °C. On the one hand, the construction of double shells could significantly increase the proportion of active species (Mn⁴⁺, Fe³⁺, Ce³⁺ and O_ads) and the interface effect between the shell layers could effectively enhance the interaction between metal oxides. On the other hand, the construction of double shells could achieve an appropriate balance between the redox capacity of the catalyst and surface acidity. Simultaneously, in situ DRIFT spectroscopy indicated that the yolk-shell MnFe@CeO_x@TiO_x-40 nanocages mainly followed the L-H mechanism during the NH₃-SCR reaction. Finally, this double-shell structure strategy provided a new idea for constructing a Mn-based catalyst with a wide temperature window and better low-temperature water resistance.

CO2 bubble-assisted in-situ construction of mesoporous Co-doped Cu2(OH)2CO3 nanosheets as advanced electrodes towards fast and highly efficient electrochemical reduction of nitrate to N2 in wastewater

The development of high-efficient and cost-effective electrocatalysts is crucial to remove nitrate pollutant in wastewater. Herein, we design and prepare mesoporous Co-doped Cu₂(OH)₂CO₃ malachite nanosheets as an electrocatalyst toward highly efficient nitrate reduction using a facile CO₂ bubble-assisted coprecipitation synthesis. The electrocatalytic performance is subject to the Co/Cu ratio of this malachite. Remarkably, compared with the pristine monometal Cu or Co-based electrocatalyst, the optimal electrocatalyst, 0.3Co@Cu₂(OH)₂CO₃, displays fast and highly efficient removal capacity of nitrate with an impressive high total nitrogen (TN) removal of 8628.99 mg N g^-1_CoCu (398.79 mg N g_cat^-1 h^-1), N₂ selectivity of 97.11% as well as negligible nitrite product at 100 mg L^-1 NO₃^--N and 2000 mg L^-1 Cl^- neutral electrolyte. Above all, high total nitrogen removal efficiency (81.92%) and chemical oxygen demand (73.74%) in actual wastewater. Its excellent electrocatalytic performance is achieved by regulating the electronic structure and the adsorption/desorption of the intermediate. This study discovers a new type of electrode materials for nitrate removal in wastewater.

Effect of CaCO3 on catalytic activity of Fe–Ce/Ti catalysts for NH3-SCR reaction

In the present work, fresh and Ca poisoned Fe–Ce/Ti catalysts were prepared and used for the NH₃-SCR reaction to investigate the effect of Ca doping on the catalytic activity of catalysts. And these catalysts were characterized by BET, XRD, Raman, UV-vis DRS, XPS, H₂-TPR, and NH₃-TPD techniques. The obtained results demonstrate that Ca doping could lead to an obvious decrease in the catalytic activity of catalysts. The reasons for this may be due to the smaller specific surface area and pore volume, the decreased ratio of Fe³⁺/Fe²⁺ and Ce³⁺/Ce⁴⁺, as well as the reduced redox ability and surface acidity.

In the present work, fresh and Ca poisoned Fe–Ce/Ti catalysts were prepared and used for the NH₃-SCR reaction to investigate the effect of Ca doping on the catalytic activity of catalysts.