Novel manganese oxide confined interweaved titania nanotubes for the low-temperature Selective Catalytic Reduction (SCR) of NO x by NH 3

Insight into the synergism between MnO2 and acid sites over Mn-SiO2@TiO2 nano-cups for low-temperature selective catalytic reduction of NO with NH3

The rational synthesis of low-temperature catalysts with high catalytic activity and stability is highly desirable for the selective catalytic reduction of NO with NH3. Here we synthesized a Mn-SiO2/TiO2 nano-cup catalyst via the coating of the mesoporous TiO2 layers on SiO2 spheres and subsequent inlay of MnO2 nanoparticles in the narrow annulus. This catalyst exhibited superior catalytic SCR activities and stability for low-temperature selective catalytic reduction of NO with NH3, with NO conversion of ∼100%, N2 selectivity above 90% at a temperature ∼140 °C. The characterization results, such as BET, XRD, H2-TPR, O2/NH3-TPD and XPS, indicated that this nano-cup structure catalyst possesses high concentration and dispersion of Mn4+ active species, strong chemisorbed O- or O2 2- species and highly stable MnO X active components over the annular structures of the TiO2 shell and SiO2 sphere, and thus enhanced the low-temperature SCR performance.

Facile fabrication of shape-controlled CoxMnyOβ nanocatalysts for benzene oxidation at low temperatures

We report a new strategy for the design and construction of Co_xMn_yO_β for C₆H₆ oxidation, a representative VOC.

Triple-shelled NiMn2O4 hollow spheres as an efficient catalyst for low-temperature selective catalytic reduction of NOx with NH3

Unique triple-shelled NiMn₂O₄ hollow spheres are fabricated by a facile solvothermal method.

Exposed metal oxide active sites on mesoporous titania channels: a promising design for low-temperature selective catalytic reduction of NO with NH3

A subtle catalyst is designed with CuO and MnO₂ active centers on the surface of mesoporous titania for low-temperature SCR.

The promoting effect of noble metal (Rh, Ru, Pt, Pd) doping on the performances of MnOx–CeO2/graphene catalysts for the selective catalytic reduction of NO with NH3at low temperatures

Rh, Ru, Pt or Pd doping on MnOx–CeO₂/graphene catalysts increased the amount of chemisorbed oxygen and surface acid sites.

High N2 selectivity in selective catalytic reduction of NO with NH3 over Mn/Ti–Zr catalysts

A series of Mn-based catalysts were prepared by a wet impregnation method for the selective catalytic reduction (SCR) of NO with NH₃. The Mn/Ti–Zr catalyst had more surface area, Lewis acid sites, and Mn⁴⁺ on its surface, and showed excellent activity and high N₂ selectivity in a wide temperature range. NH₃ and NO oxidation was investigated to gain insight into NO reduction and N₂O formation. The formation of N₂O was primarily dominated by the reaction of NO with NH₃ in the presence of O₂via the Eley–Rideal mechanism. An intimate synergistic effect existed between the Mn-based and the Ti–Zr support. It was demonstrated that the Ti–Zr support greatly promoted the catalytic performance of Mn-based catalysts.

The Ti–Zr support greatly promotes the catalytic performance of Mn-based catalysts.

Mesoporous Mn–Ti amorphous oxides: a robust low-temperature NH3-SCR catalyst

Mn–Ti amorphous oxides prepared by the combinedin situdeposition and freeze-drying strategy exhibited excellent activities and stability in low-temperature NH₃-SCR.

Design and Properties of Confined Nanocatalysts by Atomic Layer Deposition

Governing the process and outcome of chemical reactions is the most important aim of catalytic chemistry. The confinement of active sites inside nanosized spaces provides a powerful strategy to achieve this goal. Reacting molecules (reactants, intermediates, and products of a reaction) and nanomaterials (metal/metal-oxide nanoparticles) confined inside nanoreactors have been observed to exhibit modified behaviors and properties with respect to their unconfined counterparts. Typically, catalysts confined in zeolites, mesoporous materials, metal-organic frameworks, and nanotubes are obtained by traditional liquid-phase methods. However, excess metals or undesired solvents and other reagents must be removed. It is also difficult to precisely regulate the confined nanostructures and assemble multifunctional sites in the confined nanospaces. Atomic layer deposition (ALD) provides a controllable method to fabricate confined catalysts due to its outstanding advantages. In this Account, we describe our progress in the design and properties of confined nanocatalysts by ALD. ALD is an elegant method to directly deposit highly dispersed metal or oxide species into porous materials, including zeolites and mesoporous materials. We deposited Pt nanoclusters in the micropores of a KL zeolite with precisely controlled size by ALD. We also introduced CoO_x nanoclusters into mesoporous SBA-15. We have reported pioneering works on the synthesis of confined nanoparticles with metal-in-nanotube structures by a template-assisted ALD method. Confined Cu nanoparticles were prepared by reducing CuO nanowires coated with Al₂O₃, TiO₂, or alucone layers by ALD. Confined Cu and Au nanoparticles were also prepared starting from the corresponding metal nanowires with the assistance of sacrificial layers produced by ALD. In a more facile strategy, Au nanoparticles confined in Al₂O₃ nanotubes were produced using a sacrificial template by ALD. Furthermore, we synthesized a multiply confined Ni-based nanocatalyst through a template-assisted ALD method. We assembled multiple interfaces (Ni/Al₂O₃ and Pt/TiO₂) in a confined nanospace for tandem reactions by template-assisted ALD. The synergistic effect of two interfaces enhanced the tandem reaction, and the confined nanospace favored the instant transfer of intermediates between the two interfaces. In addition, porous TiO₂ nanotubes with spatially separated Pt and CoO_x cocatalysts were also produced by ALD. The confined catalysts can be further treated by ALD. We used ALD to modify the mesoporous SBA-15 support to precisely tune the active species-support interaction. In addition to the support, the confined metal nanoparticles can also be coated with an ultrathin oxide layer by ALD to further improve their catalytic activities. Moreover, the structure and size of the confined nanospace can be tuned precisely by ALD. Overall, ALD has exhibited noteworthy applications in and will provide new opportunities for the design and synthesis of highly effective confined catalysts.

Rationally Designed Porous MnOx-FeOx Nanoneedles for Low-Temperature Selective Catalytic Reduction of NOx by NH3

In this work, a novel porous nanoneedlelike MnO_x-FeO_x catalyst (MnO_x-FeO_x nanoneedles) was developed for the first time by rationally heat-treating metal-organic frameworks including MnFe precursor synthesized by hydrothermal method. A counterpart catalyst (MnO_x-FeO_x nanoparticles) without porous nanoneedle structure was also prepared by a similar procedure for comparison. The two catalysts were systematically characterized by scanning and transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, ammonia temperature-programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFT), and their catalytic activities were evaluated by selective catalytic reduction (SCR) of NO_x by NH₃. The results showed that the rationally designed MnO_x-FeO_x nanoneedles presented outstanding low-temperature NH₃-SCR activity (100% NO_x conversion in a wide temperature window from 120 to 240 °C), high selectivity for N₂ (nearly 100% N₂ selectivity from 60 to 240 °C), and excellent water resistance and stability in comparison with the counterpart MnO_x-FeO_x nanoparticles. The reasons can be attributed not only to the unique porous nanoneedle structure but also to the uniform distribution of MnO_x and FeO_x. More importantly, the desired Mn⁴⁺/Mnⁿ⁺ and O_α/(O_α + O_β) ratios, as well as rich redox sites and abundant strong acid sites on the surface of the porous MnO_x-FeO_x nanoneedles, also contribute to these excellent performances. In situ DRIFT suggested that the NH₃-SCR of NO over MnO_x-FeO_x nanoneedles follows both Eley-Rideal and Langmuir-Hinshelwood mechanisms.

Comparison of titania nanotubes and titanium dioxide as supports of low-temperature selective catalytic reduction catalysts under sulfur dioxide poisoning

A series of iron-manganese oxide catalysts supported on TiO₂ and titanium nanotubes (TNTs) were studied for low temperature selective catalytic reduction (SCR) of NO with NH₃ in the presence of SO_2. The results showed that the specific surface area and the amount of Brønsted acid sites were highly correlated. The results also demonstrated that higher Mn⁴⁺/Mn³⁺ ratios and larger specific surface areas might be the main reasons for the excellent performance of MnFe-TNTs catalyst after SO₂ poisoning. The SO₂ poisoning effect could be minimized by reducing the GHSV, increasing the reaction temperature, or increasing the [NH₃]/[NO] molar ratio. The results also indicated that the formation of ammonium sulfate had a stronger effect on the NO conversion efficiency as compared to the formation of metal sulfate. Thus operating the low temperature SCR at above 230 ^oC to avoid the formation of ammonium sulfate would be the priority choice when SO₂ poisoning is a concerned issue. Implications: Low-temperature selective catalytic reduction (SCR) has attracted increasing attention due to that it can reduce the energy consumption for the SCR process employed in industries such as steel plants and glass manufacturing plants. However, it also suffers from the sulfur dioxide (SO₂) poisoning problem. This study investigates the possibility of using titania nanotubes (TNTs) as the support of Mn/Fe bimetal oxide catalysts for low-temperature SCR to reduce the SO₂ poisoning. The results indicated that the MnFe-TNT catalyst can tolerate SO₂ for a longer time as compared with the MnFe-TiO₂ catalyst.

Manganese-rich MnSAPO-34 molecular sieves as an efficient catalyst for the selective catalytic reduction of NO x with NH3: one-pot synthesis, catalytic performance, and characterization

Manganese-rich MnSAPO-34 molecular sieves were prepared by one-pot synthesis method for NO _x abatement using the ammonia-selective catalytic reduction (NH₃-SCR) technology and characterized using ICP, BET, XRD, FE-SEM, H₂-TPR, NH₃-TPD, XPS, and DR UV-Vis analyses. The experimental results indicate that the Mn content and chemical state, as well as the surface acidity, of the MnSAPO-34 molecular sieves significantly enhance their DeNO _x efficiency at low temperatures (ca. 200-300 °C). The manganese-rich MnSAPO-34 was synthesized using a combination of triethylamine and diisopropylamine as the structural directing agents and high Mn loading (n(MnO)/n(P₂O₅) = 0.4). The resulting catalyst exhibits the highest activity among all of the samples with a NO _x conversion value of nearly 95% and a N₂ selectivity that is higher than 90% at 220-400 °C. In addition, this catalyst presents higher NO _x conversion than the conventional V₂O₅-WO₃/TiO₂ catalysts and other SAPO-based catalysts below 300 °C. Furthermore, the analytical results indicate that the manganese species in the catalyst are mainly in the form of a framework Mn(IV), which could play a significant role in the NH₃-SCR process as the specific active species. The results suggest that controlling the types and content of the organic amine templates and variations in the surface acidity of the catalysts may significantly enhance the SCR activity at lower temperatures.

Facile preparation of high-performance Fe-doped Ce–Mn/TiO2 catalysts for the low-temperature selective catalytic reduction of NOx with NH3

A Ce–Mn–Fe/TiO₂ catalyst has been successfully prepared using a single impregnation method with excellent low-temperature NH₃-SCR activity.

The enhanced resistance to P species of an Mn–Ti catalyst for selective catalytic reduction of NOx with NH3 by the modification with Mo

The modification of Mn–Ti catalyst by Mo could enhance its resistance to P species.

Influence of tungsten on the NH3-SCR activity of MnWOx/TiO2 catalysts

A series of bulk MnWO_x and supported MnWO_x/TiO₂ catalysts with MnWO₄ structure were prepared via self-propagating high-temperature synthesis (SHS), co-precipitation and impregnation methods.

A comparative study of manganese–cerium doped metal–organic frameworks prepared via impregnation and in situ methods in the selective catalytic reduction of NO

Impregnation and in situ doping were applied for the preparation of MnCe loaded MOFs and the behavior of the catalysts in the SCR was investigated.

Promotional effect of the TiO2 (001) facet in the selective catalytic reduction of NO with NH3: in situ DRIFTS and DFT studies

NO on anatase-TiO₂ (001) was mainly in the form of NO₂ which could trigger the subsequent ‘fast SCR’ reaction.

Novel Fe–Ce–Ti catalyst with remarkable performance for the selective catalytic reduction of NOx by NH3

The redox cycle (Ce⁴⁺ + Fe²⁺ ↔ Ce³⁺ + Fe³⁺) over the Fe–Ce–Ti catalyst contributes to the activation of NO_x and NH₃ and thus the formation of reaction intermediates, leading to the high catalytic performance for the NH₃-SCR of NO_x.

A novel Ce–Sb binary oxide catalyst for the selective catalytic reduction of NOx with NH3

The synergetic effect between Sb and Ce not only increases the surface acidity of the catalyst but also enhances the redox property, both of which contribute to improving NH₃-SCR activity.

MnOx supported on a TiO2@SBA-15 nanoreactor used as an efficient catalyst for one-pot synthesis of imine by oxidative coupling of benzyl alcohol and aniline under atmospheric air

Mesoporous silica (SBA-15) encapsulated TiO₂ nanoreactor used as support for MnOx and it (MnOx/TiO₂@SBA-15) acts as catalyst for the one-pot synthesis of imine by oxidative coupling between benzyl alcohol & aniline in the presence of atmospheric air.

Modification of MnCo2Ox catalysts by NbOx for low temperature selective catalytic reduction of NO with NH3

Among the NbOx modified MnCo₂Ox catalysts by co-precipitation, MnCo₂Nb_0.5Ox presented high activity, N₂ selectivity and H₂O resistance for NH₃-SCR reaction at low temperatures.

Morphology-dependent performance of Zr–CeVO4/TiO2 for selective catalytic reduction of NO with NH3

The morphology-dependent performance of Zr–CeVO₄/TiO₂ was demonstrated for the selective catalytic reduction of NO with NH₃.