Denitrification activity test of a V modified Mn-based ceramic filter

In view of the characteristics of high temperature denitrification and low water and sulfur resistance of single manganese-based catalysts, a vanadium-manganese-based ceramic filter (VMA(14)-CCF) was prepared by the impregnation method modified with V. The results showed that the NO conversion of VMA(14)-CCF was more than 80% at 175-400 °C. At 225-300 °C, the conversion of NO can reach 100%. High NO conversion and low pressure drop can be maintained at all face velocities. The resistance of VMA(14)-CCF to water, sulfur and alkali metal poisoning is better than that of a single manganese-based ceramic filter. XRD, SEM, XPS and BET were further used for characterization analysis. The introduction of V protects the MnO_x center, promotes the conversion of Mn³⁺ to Mn⁴⁺, and provides abundant surface adsorbed oxygen. The development of VMA(14)-CCF greatly broadens the application range of ceramic filters in denitrification.

A review on identification, quantification, and transformation of active species in SCR by EPR spectroscopy

Electron paramagnetic resonance (EPR) is the only technique that provides direct detection of free radicals and samples that contain unpaired electrons. Thus, EPR had an important potential application in the field of selective catalytic reduction of nitrogen oxide (SCR). For the first time, this work reviewed recent developments of EPR in charactering SCR. First, qualitative analysis focused on recognizing Cu, Fe, V, Ti, Mn, and free-radical (oxygen vacancy and superoxide radical) species. Second, quantification of the active species was obtained by a double-integral and calibration method. Third, the active species evolved because of different thermal treatments and redox-thermal processes under reductants (NH₃ and NO). The coordination information of the active species in catalysts and their effects on SCR performances were concluded from mechanism viewpoints. Finally, potential perspectives were put forward for EPR developments in characterizing the SCR processes in the future. After all, EPR characterization will help to have a deep understanding of structure-activity relationship in one catalyst.

Oxygen Defect Engineering of β-MnO2 Catalysts via Phase Transformation for Selective Catalytic Reduction of NO

The catalysts for low-temperature selective catalytic reduction of NO with NH₃ (NH₃ -SCR) are highly desired due to the large demand in industrial furnaces. The characteristic of low-temperature requires the catalyst with rich active sites especially the redox sites. Herein, the authors obtain oxygen defect-rich β-MnO₂ from a crystal phase transformation process during air calcination, by which the as-prepared γ-MnO₂ nanosheet and nanorod can be conformally transformed into the corresponding β-MnO₂ . Simultaneously, this transformation accompanies oxygen defects modulation resulted from lattice rearrangement. The most active β-MnO₂ nanosheet with plentiful oxygen defects shows a high efficiency of > 90% NO conversion in an extremely wide operation window of ≈120-350 °C. The detailed characterizations and density functional theory (DFT) calculations reveal that the introduction of oxygen defects enhances the adsorption properties for reactants and decreases the energy barriers of *NH₂ formation more than 0.3 eV (≈0.32-0.37 eV), which contributes to a high efficiency of low-temperature SCR activity. The authors finding provides a feasible approach to achieve the oxygen defect engineering and gains insight into manganese-based catalysts for low-temperature NO removal or pre-oxidation.

Effect of Formaldehyde in Selective Catalytic Reduction of NOx by Ammonia (NH3-SCR) on a Commercial V2O5-WO3/TiO2 Catalyst under Model Conditions

The impact of formaldehyde (HCHO, formed in vehicle exhaust gases by incomplete combustion of fuel) on the performance of a commercial V₂O₅-WO₃/TiO₂ catalyst in NH₃-SCR of NO_x under dry conditions has been analyzed in detail by catalytic tests, in situ FTIR and transient studies using temporal analysis of products (TAP). HCHO reacts preferentially with NH₃ to a formamide (HCONH₂) surface intermediate. This deprives NH₃ partly from its desired role as a reducing agent in the SCR and diminishes NO conversion and N₂ selectivity. Between 250 and 400 °C, HCONH₂ decomposes by dehydration (major pathway) and decarbonylation (minor pathway) to liberate toxic HCN and CO, respectively. HCN was proven to be oxidized by lattice oxygen of the catalyst to CO₂ and NO, which enters the NH₃-SCR reaction.

Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV-Vis/ATR-IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas-Liquid Phase Reactions

Operando EPR, XANES/EXAFS, UV‐Vis and ATR‐IR spectroscopic methods have been coupled for the first time in the same experimental setup for investigation of unclear mechanistic aspects of selective aerobic oxidation of benzyl alcohol by a Cu/TEMPO catalytic system (TEMPO=2,2,6,6‐tetramethylpiperidinyloxyl). By multivariate curve resolution with alternating least‐squares fitting (MCR‐ALS) of simultaneously recorded XAS and UV‐Vis data sets, it was found that an initially formed (bpy)(NMI)Cu^I‐ complex (bpy=2,2′‐bipyridine, NMI=N‐methylimidazole ) is converted to two different Cu^II species, a mononuclear (bpy)(NMI)(CH₃CN)Cu^II‐OOH species detectable by EPR and ESI‐MS, and an EPR‐silent dinuclear (CH₃CN)(bpy)(NMI)Cu^II(μ‐OH)₂⋅Cu^II (bpy)(NMI) complex. The latter is cleaved in the further course of reaction into (bpy)(NMI)(HOO)Cu^II‐TEMPO monomers that are also EPR‐silent due to dipolar interaction with bound TEMPO. Both Cu monomers and the Cu dimer are catalytically active in the initial phase of the reaction, yet the dimer is definitely not a major active species nor a resting state since it is irreversibly cleaved in the course of the reaction while catalytic activity is maintained. Gradual formation of non‐reducible Cu^II leads to slight deactivation at extended reaction times.

MnO2–GO-scroll–TiO2–ITQ2 as a low-temperature NH3-SCR catalyst with a wide SO2-tolerance temperature range

GO-scroll–TiO₂–ITQ2 improved the steam-resistance and SO₂-resistance of the low-temperature manganese-based NH₃-SCR catalyst.