Mechanism and regeneration of sulfur-poisoned Mn-promoted calcined NiAl hydrotalcite-like compounds for C3H6-SCR of NO

The selective catalytic reduction of NO with propene (C₃H₆-SCR) in the presence of SO₂ was investigated over a series of Mn-promoted calcined NiAl hydrotalcite-like compounds. The obtained 5% MnNiAlO catalyst exhibits superior NO conversion efficiency (95%) at 240 °C, and excellent sulfur-poisoning resistance. The possible reaction pathways of the catalytic process were proposed according to several characterization measurements. It is demonstrated that Mn-promoted NiAlO catalysts enhance the Brønsted acid sites and surface active oxygen groups, and improve the redox properties by the redox cycle (Ni³⁺ + Mn²⁺ ↔ Ni²⁺ + Mn⁴⁺). Thus, the amount of the reaction intermediates is improved, and the reactivities between C_xH_yO_z species and nitrite/nitrate species are promoted. Furthermore, in the presence of SO₂, the MnNiAlO samples can give rise to minor formation of sulfate and inhibit the competitive adsorption effectively due to their nitrite/nitrate species being more abundant and stable. Finally, regeneration was studied using in situ FTIR and the water washing method showed the best performance on the regeneration of S-poisoned catalysts.

The selective catalytic reduction of NO with propene (C₃H₆-SCR) in the presence of SO₂ was investigated over a series of Mn-promoted calcined NiAl hydrotalcite-like compounds.     

Combustion of lean methane over Co3O4 catalysts prepared with different cobalt precursors

To investigate the effect of catalyst precursors on physicochemical properties and activity of lean methane catalytic combustion, a series of Co₃O₄ catalysts were prepared via a precipitation method by using four different cobalt precursors: Co(C₂H₃O₂)₂, Co(NO₃)₂, CoCl₂, and CoSO₄. The catalysts were characterized by BET, XRD, SEM, Raman, XPS, XRF, O₂-TPD and H₂-TPR techniques. It was found that the different types of cobalt precursor had remarkable effects on the surface area, particle size, reducibility and catalytic performance. In contrast, the Co₃O₄-Ac catalyst showed a relatively small surface area, but its activity and stability were the highest. XPS, Raman, O₂-TPD and H₂-TPR results demonstrated that the superior catalytic performance of Co₃O₄-Ac was associated with its higher Co²⁺ concentration, more surface active oxygen species and better reducibility. In addition, the activity of the Co₃O₄-S catalyst reduced significantly due to the residual impurity SO₄²⁻, which could reduce the concentration of surface adsorbed active oxygen species and inhibit oxygen migration.

The effects of cobalt precursor on the microstructure, surface properties, reducibility and catalytic performance for methane combustion were investigated.     

Sm2O3/Co3O4 catalysts prepared by dealloying for low-temperature CO oxidation

A series of Co₃O₄ catalysts modified by Sm were prepared by a combined dealloying and calcination approach, and the catalytic activities were evaluated using CO catalytic oxidation. The Sm₂O₃/Co₃O₄ catalysts were composed of a large number of nanorods and nanosheets, and exhibited a three-dimensional supporting structure with pores. The experimental results revealed that the addition of a small amount of Sm into the precursor AlCo alloy led to a dealloyed sample with improved catalytic activity, and the dealloyed Al₉₀Co_9.5Sm_0.5 ribbons (0.5 Sm₂O₃/Co₃O₄) calcined at 300 °C showed the highest activity for CO oxidation with complete CO conversion at 135 °C, moreover, CO conversion almost no attenuation, even after 70 hours of catalytic oxidation, which is superior to that of Co₃O₄. The enhanced catalytic activity of the Sm₂O₃/Co₃O₄ catalyst can be attributed to the large specific surface area, more reactive oxygen species and Co³⁺ ion, as well as electronic interactions between Sm and Co.

A series of Co₃O₄ catalysts modified by Sm were prepared by a combined dealloying and calcination approach, and the catalytic activities were evaluated using CO catalytic oxidation.     

Recent advances in supported molecular sieve catalysts with wide temperature range for selective catalytic reduction of NOX with C3H6

NO_X is a major atmospheric pollutant that is emanated by motor vehicles, thermal power plants, and industrial boilers. Therefore, the removal of NO_X is a research hotspot in the exhaust gas treatment field. Numerous methods have been used to eliminate NO_X: the selective catalytic reduction of NO_X using C₃H₆ as the reducing agent (C₃H₆-SCR) is an effective method to remove NO_X. The key issue in NO_X removal in C₃H₆-SCR is to obtain catalysts with low-temperature activity and wide operating temperatures. Till date, different supported wide-temperature-active molecular sieve catalysts have been prepared and used in C₃H₆-SCR reactions. Studies have shown that the catalytic performance of supported catalysts is related not only to the active component but also to the structural and textural parameters of the molecular sieve supports. This review summarizes the structural and textural characteristics, catalytic properties, and catalytic mechanism of molecular sieve catalysts with different pore structures for C₃H₆-SCR reactions. The design strategies of supported molecular sieve catalysts are suggested. The goal of this review is to highlight (1) the structural and textural characteristics and low-temperature catalytic performance of different supported molecular sieve catalysts; (2) the relationship between wide-temperature window and loaded active components, as well as carriers of the supported molecular sieve catalysts; and (3) design strategies and development prospects of supported molecular sieve catalysts with low-temperature activity and wide-temperature operating range for C₃H₆-SCR reactions.

NO_X is a major atmospheric pollutant that is emanated by motor vehicles, thermal power plants, and industrial boilers.     

Mn-based catalysts supported on γ-Al2O3, TiO2 and MCM-41: a comparison for low-temperature NO oxidation with low ratio of O3/NO

Mn-Based catalysts supported on γ-Al₂O₃, TiO₂ and MCM-41 synthesized by an impregnation method were compared to evaluate their NO catalytic oxidation performance with low ratio O₃/NO at low temperature (80–200 °C). Activity tests showed that the participation of O₃ remarkably promoted the NO oxidation. The catalytic oxidation performance of the three catalysts decreased in the following order: Mn/γ-Al₂O₃ > Mn/TiO₂ > Mn/MCM-41, indicating that Mn/γ-Al₂O₃ exhibited the best catalytic activity. In addition, there was a clear synergistic effect between Mn/γ-Al₂O₃ and O₃, followed by Mn/TiO₂ and O₃. The characterization results of XRD, EDS mapping, BET, H₂-TPR, XPS and TG showed that Mn/γ-Al₂O₃ had good manganese dispersion, excellent redox properties, appropriate amounts of coexisting Mn³⁺ and Mn⁴⁺ and abundant chemically adsorbed oxygen, which ensured its good performance. In situ DRIFTS demonstrated the NO adsorption performance on the catalyst surface. As revealed by in situ DRIFTS experiments, the chemically adsorbed oxygen, mainly from the decomposition of O₃, greatly promoted the NO adsorption and the formation of nitrates. The Mn-based catalysts showed stronger adsorption strength than the corresponding pure supports. Due to the abundant adsorption sites provided by pure γ-Al₂O₃, under the interaction of Mn and γ-Al₂O₃, the Mn/γ-Al₂O₃ catalyst exhibited the strongest NO adsorption performance among the three catalysts and produced lots of monodentate nitrates (–O–NO₂) and bidentate nitrates (–O₂NO), which were the vital intermediate species for NO₂ formation. Moreover, the NO–TPD studies also demonstrated that Mn/γ-Al₂O₃ showed the best NO desorption performance among the three catalysts. The good NO adsorption and desorption characteristics of Mn/γ-Al₂O₃ improved its high catalytic activity. In addition, the activity test results also suggested that Mn/γ-Al₂O₃ exhibited good SO₂ tolerance.

The Mn/γ-Al₂O₃ catalyst exhibited excellent performance for NO conversion in the presence of a low ratio of O₃/NO, which was due to the coexistence of Mn³⁺ and Mn⁴⁺ and abundant chemically adsorbed oxygen.     

Metal–organic framework-derived CeO2–ZnO catalysts for C3H6-SCR of NO: an in situ DRIFTS study

Metal–organic framework (MOF)-based derivatives have attracted an increasing interest in various research fields. Here, we synthesized CeO₂–ZnO catalysts through the complete thermal decomposition of the Ce/MOF-5 precursor. The catalysts were characterized using XRD, FTIR, TG-DSC, SEM and H₂-TPR. It is found that the as-prepared CeO₂–ZnO is favorable for strengthening the interaction between Ce⁴⁺ and Zn²⁺. A significant improvement in the catalytic performance for C₃H₆-SCR of NO was found over the Ce-doped catalysts with the highest N₂ yield of 69.1% achieved over 5% CeO₂–ZnO. In situ DRIFTS and NO-TPD experiments demonstrated the formation of monodentate nitrates, bidentate nitrates, chelating nitrite, nitro compounds, nitrosyl and C_xH_yO_z species (enolic species and acetate) on the surface, followed by the formation of hydrocarbonate or carbonate as intermediates to directly generate N₂, CO₂ and H₂O.

Metal–organic framework (MOF)-based derivatives have attracted an increasing interest in various research fields. Here, we synthesized CeO₂–ZnO catalysts through the complete thermal decomposition of the Ce/MOF-5 precursor.     

Mesoporous MnOx–CeO2 composites for NH3-SCR: the effect of preparation methods and a third dopant

In this study, different preparation methods including an oxalate route, a nano-casting strategy and a traditional co-precipitation route were applied to obtain MnOx–CeO₂ mixed oxides for selective catalytic reduction (SCR) of NO with NH₃. The catalyst prepared from the oxalate route showed improved performance for NOx conversion and SO₂ + H₂O durability. To further improve the SO₂ and H₂O resistance of catalysts, ternary oxides were prepared from the oxalate route. The catalysts were studied by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (H₂-TPR), NH₃ temperature-programmed desorption (NH₃-TPD), SO₂ temperature-programmed desorption (SO₂-TPD), and in situ diffuse reflectance infrared fourier transform spectroscopy (in situ DRIFTS). The nickel–manganese–cerium ternary oxide showed the best SO₂ and H₂O durability. The reason can be ascribed to its smaller pores, amorphous structure, and moderate amount of surface Mn³⁺/oxygen species, which could decrease chemical adsorption of SO₂.

In this study, an optimal oxalate route was used to obtain nickel/cobalt doped MnOx–CeO₂ mixed oxides. Nickel doped MnOx–CeO₂ showed excellent NH₃-SCR activity and H₂O + SO₂ resistance.     

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.     

Improvement of low-temperature NH3-SCR catalytic performance over nitrogen-doped MOx–Cr2O3–La2O3/TiO2–N (M = Cu,Fe, Ce) catalysts

A series of MO_x–Cr₂O₃–La₂O₃/TiO₂–N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method. Comparing the low-temperature NH₃-SCR activity of the catalysts, CeCrLa/Ti–N (xCeO₂–yCr₂O₃–zLa₂O₃/TiO₂–N) exhibited the best catalytic performance (NO conversion approaching 100% at 220–460 °C). The physico-chemical properties of the catalysts were characterized by XRD, BET, SEM, XPS, H₂-TPR, NH₃-TPD and in situ DRIFTS. From the XRD and SEM results, N doping affects the crystalline growth of anatase TiO₂ and MO_x (M = Cu, Fe, Ce, Cr, La) which were well dispersed over the support. Moreover, the doping of N promotes the increase of the Cr⁶⁺/Cr ratio and Ce³⁺/Ce ratio, and the surface chemical adsorption oxygen content, which suggested the improvement of the redox properties of the catalyst. And the surface acid content of the catalyst increased with the doping of N, which is related to CeCrLa/TiO₂–N having the best catalytic activity at high temperature. Therefore, the CeCrLa/TiO₂–N catalyst exhibited the best NH₃-SCR performance and the redox performance of the catalysts is the main factor affecting their activity. Furthermore, in situ DRIFTS analysis indicates that Lewis-acid sites are the main adsorption sites for ammonia onto CeCrLa/TiO₂–N and the catalyst mainly follows the L–H mechanism.

A series of MO_x–Cr₂O₃–La₂O₃/TiO₂–N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method.     

Synthesis of CrOx/C catalysts for low temperature NH3-SCR with enhanced regeneration ability in the presence of SO2

Chromium oxide nano-particles with an average diameter of 3 nm covered by amorphous carbon (CrO_x/C) were successfully synthesized. The synthesized CrO_x/C materials were used for the selective catalytic reduction of NO_x by NH₃ (NH₃-SCR), which shows superb NH₃-SCR activity and in particular, satisfactory regeneration ability in the presence of SO₂ compared with Mn-based catalysts. The as-prepared catalysts were characterized by XRD, HRTEM, Raman, FTIR, BET, TPD, TPR, XPS and in situ FTIR techniques. The results indicated presence of certain amounts of unstable lattice oxygen exposed on the surface of CrO_x nano-particles with an average size of 3 nm in the CrO_x/C samples, which led to NO being conveniently oxidized to NO₂. The formed NO₂ participated in NH₃-SCR activity, reacting with catalysts via a “fast NH₃-SCR” pathway, which enhanced th NH₃-SCR performance of the CrO_x/C catalysts. Furthermore, the stable lattice of the CrO_x species made the catalyst immune to the sulfation process, which was inferred to be the cause of its superior regeneration ability in the presence of SO₂. This study provides a simple way to synthesize stable CrO_x nano-particles with active oxygen, and sheds light on designing NH₃-SCR catalysts with highly efficient low temperature activity, SO₂ tolerance, and regeneration ability.

Novel CrO_x@C catalyst with both remarkable NH₃-SCR activity and satisfactory regeneration ability in the presence of SO₂.     

Promotion effect of urchin-like MnOx@PrOx hollow core–shell structure catalysts for the low-temperature selective catalytic reduction of NO with NH3

A MnO_x@PrO_x catalyst with a hollow urchin-like core–shell structure was prepared using a sacrificial templating method and was used for the low-temperature selective catalytic reduction of NO with NH₃. The structural properties of the catalyst were characterized by FE-SEM, TEM, XRD, BET, XPS, H₂-TPR and NH₃-TPD analyses, and the performance of the low-temperature NH₃-SCR was also tested. The results show that the catalyst with a molar ratio of Pr/Mn = 0.3 exhibited the highest NO conversion at nearly 99% at 120 °C and NO conversion greater than 90% over the temperature range of 100–240 °C. Also, the MnO_x@PrO_x catalyst presented desirable SO₂ and H₂O resistance in 100 ppm SO₂ and 10 vol% H₂O at the space velocity of 40 000 h⁻¹ and a testing time of 3 h test at 160 °C. The excellent low-temperature catalytic activity of the catalyst could ultimately be attributed to high concentrations of Mn⁴⁺ and adsorbed oxygen species on the catalyst surface, suitable Lewis acidic surface properties, and good reducing ability. Additionally, the enhanced SO₂ and H₂O resistance of the catalyst was primarily ascribed to its unique core–shell structure which prevented the MnO_x core from being sulfated.

A MnO_x@PrO_x catalyst with a hollow urchin-like core–shell structure was prepared using a sacrificial templating method and was used for the low-temperature selective catalytic reduction of NO with NH₃.     

Simple fabrication of Co3O4 nanoparticles on N-doped laser-induced graphene for high-performance supercapacitors

This study demonstrates a simple strategy to fabricate Co₃O₄ on N-doped laser-induced graphene (Co₃O₄-NLIG) based on duplicate laser pyrolysis, enabling the in situ generation of Co₃O₄ nanoparticles and heteroatom doping in laser-induced graphene (LIG). Morphological analyses reveal the uniform distribution of Co₃O₄ nanoparticles on the surface of the LIG structure. The modification of NLIG with Co₃O₄ nanoparticles results in impressive electrochemical performance due to the contributions from electric double-layer capacitance and pseudocapacitance. The optimal Co₃O₄-NLIG is produced at 20 wt% cobalt precursor loading (Co₃O₄-NLIG-20). In a three-electrode setup, this electrode exhibits a specific areal capacitance (C_A) of 216.3 mF cm⁻² at a current density of 0.5 mA cm⁻² in a 1 M KOH electrolyte. When the optimal electrodes are assembled into a solid-state supercapacitor (Co₃O₄-NLIG-SC) using a poly(vinyl alcohol) phosphoric acid (PVA–H₃PO₄) gel electrolyte, a C_A of 17.96 mF cm⁻² is obtained with good cycling stability.

Simultaneous decoration of Co₃O₄ nanoparticles and heteroatom doping on laser-induced graphene based on a duplicate pyrolysis method for supercapacitor applications.     

Effect of Ni/Co mass ratio and NiO–Co3O4 loading on catalytic performance of NiO–Co3O4/Nb2O5–TiO2 for direct synthesis of 2-propylheptanol from n-valeraldehyde

In the direct synthesis of 2-propylheptanol (2-PH) from n-valeraldehyde, a second-metal oxide component Co₃O₄ was introduced into NiO/Nb₂O₅–TiO₂ catalyst to assist in the reduction of NiO. In order to optimize the catalytic performance of NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst, the effects of the Ni/Co mass ratio and NiO–Co₃O₄ loading were investigated. A series of NiO–Co₃O₄/Nb₂O₅–TiO₂ catalysts with different Ni/Co mass ratios were prepared by the co-precipitation method and their catalytic performances were evaluated. The result showed that NiO–Co₃O₄/Nb₂O₅–TiO₂ with a Ni/Co mass ratio of 8/3 demonstrated the best catalytic performance because the number of d-band holes in this catalyst was nearly equal to the number of electrons transferred in hydrogenation reaction. Subsequently, the NiO–Co₃O₄/Nb₂O₅–TiO₂ catalysts with different Ni/Co mass ratios were characterized by XRD and XPS and the results indicated that both an interaction of Ni with Co and formation of a Ni–Co alloy were the main reasons for the reduction of NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst in the reaction process. A higher NiO–Co₃O₄ loading could increase the catalytic activity but too high a loading resulted in incomplete reduction of NiO–Co₃O₄ in the reaction process. Thus the NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst with a Ni/Co mass ratio of 8/3 and a NiO–Co₃O₄ loading of 14 wt% showed the best catalytic performance; a 2-PH selectivity of 80.4% was achieved with complete conversion of n-valeraldehyde. Furthermore, the NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst showed good stability. This was ascribed to the interaction of Ni with Co, the formation of the Ni–Co alloy and further reservation of both in the process of reuse.

NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst with a Ni/Co mass ratio of 8/3 and NiO–Co₃O₄ loading of 14% shows the best catalytic performance.     

Fullerene-modified magnetic silver phosphate (Ag3PO4/Fe3O4/C60) nanocomposites: hydrothermal synthesis,characterization and study of photocatalytic,catalytic and antibacterial activities

In this work, fullerene-modified magnetic silver phosphate (Ag₃PO₄/Fe₃O₄/C₆₀) nanocomposites with efficient visible light photocatalytic and catalytic activity were fabricated by a simple hydrothermal approach. The composition and structure of the obtained new magnetically recyclable ternary nanocomposites were completely characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, Brunauer–Emmett–Teller (BET) specific surface area analysis, vibrating sample magnetometery (VSM), diffuse reflectance spectroscopy (DRS), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy and transmission electron microscopy (TEM). This novel magnetically recyclable heterogeneous fullerene-modified catalyst was tested for the H₂O₂-assisted photocatalytic degradation of MB dye under visible light. The results show that about 95% of the MB (25 mg L⁻¹, 50 ml) was degraded by the Ag₃PO₄/Fe₃O₄/C₆₀ nanocomposite within 5 h under visible light irradiation. The catalytic performance of the Ag₃PO₄/Fe₃O₄/C₆₀ nanocomposite was then examined for 4-nitrophenol (4-NP) reduction using NaBH₄. This new nanocomposite showed that 4-NP was reduced to 4-aminophenol (4-AP) in 98% yield with an aqueous solution of NaBH₄. In both photocatalytic and catalytic reactions, the Ag₃PO₄/Fe₃O₄/C₆₀ nanocomposite exhibited higher catalytic activity than pure Ag₃PO₄. Moreover, the Ag₃PO₄/Fe₃O₄/C₆₀ nanocomposite could be magnetically separated from the reaction mixture and reused without any change in structure. The antibacterial activity of the nanocomposites was also investigated and they showed good antibacterial activity against a few human pathogenic bacteria.

Fullerene-modified magnetic silver phosphate (Ag₃PO₄/Fe₃O₄/C₆₀) nanocomposites prepared by a hydrothermal route were used as photocatalysts/catalysts for the efficient degradation and reduction of MB dye and 4-nitrophenol, respectively.     

Study on the mechanism of synthetic (Ce,La)CO3F sulfuric acid acidification and NH3-SCR loaded with Mn and Fe

A hydrothermal method was used to synthesise (Ce,La)CO₃F grain simulated minerals, in accordance with the Ce–La ratio of bastnaesite in the mineralogy of the Bayan Ebo process. The NH₃-SCR catalytic activity of the synthesised (Ce,La)CO₃F was improved by loading transition metals Mn and Fe and sulphuric acid acidification treatments. The activity test results showed that the catalysts which were simultaneously acidified with sulphuric acid and loaded with transition metals Mn and Fe had a NO_x conversion of 92% at 250 °C. XRD, SEM, XPS and in situ Fourier transform infrared spectroscopy (FTIR) were used to investigate the physical phase structure, surface morphology, reaction performance and mechanism of the catalysts, to provide theoretical guidance for the specific reaction path of cerium fluorocarbon ore in the NH₃-SCR reaction. The results showed that the introduction of transition metals and sulphuric acid greatly increases the proportion of adsorbed oxygen (O_α) and facilitates the adsorption of NH₃ and NO. The catalyst surface metal sulphate and metal oxide species act as the main active components on the catalyst surface to promoted the reaction, and cracks and pores appear on the surface to facilitate the adsorption of reactive gases. The reaction mechanism of the SO₄²⁻–Mn–Fe/(Ce,La)CO₃F catalyst, and characterisation of the adsorption and conversion behaviour of the reactive species on the catalyst surface, were investigated by Fourier transform infrared spectroscopy (FTIR). The results showed that the catalyst follows the E–R and L–H mechanisms throughout the reaction, with the E–R mechanism being the main reaction. The reaction species were NH₄⁺/NH₃ species in the adsorbed state and NO. The NH₃(ad) species on the Lewis acidic site is the main NH₃(g) adsorbed species for the reaction, bonded to Ce⁴⁺ in the carrier (Ce,La)CO₃F to participate in the acid cycle reaction, and undergo a redox reaction on the catalyst surface to produce N₂ and H₂O. The SO₄²⁻ present on the catalyst surface can also act as an acidic site for the adsorption of NH₃. The above results indicated the excellent performance of the SO₄²⁻–Mn–Fe/(Ce,La)CO₃F catalyst, which provided a theoretical basis for the high value utilization of bastnaesite.

A hydrothermal method was used to synthesise (Ce,La)CO₃F grain simulated minerals, in accordance with the Ce–La ratio of bastnaesite in the mineralogy of the Bayan Ebo process.     

Selective catalytic reduction of NOx by low-temperature NH3 over MnxZr1 mixed-oxide catalysts

Mn_xZr₁ series catalysts were prepared by a coprecipitation method. The effect of zirconium doping on the NH₃-SCR performance of the MnO_x catalyst was studied, and the influence of the calcination temperature on the catalyst activity was explored. The results showed that the Mn₆Zr₁ catalyst exhibited good NH₃-SCR activity when calcined at 400 °C. When the reaction temperature was 125–250 °C, the NO_x conversion rate of Mn₆Zr₁ catalyst reached more than 90%, and the optimal conversion efficiency reached 97%. In addition, the Mn₆Zr₁ catalyst showed excellent SO₂ and H₂O resistance at the optimum reaction temperature. Meanwhile, the catalysts were characterized. The results showed that the morphology of the MnO_x catalyst was significantly changed, whereby as the proportion of Mn⁴⁺ and O_α species increased, the physical properties of the catalyst were improved. In addition, both Lewis acid sites and Brønsted acid sites existed in the Mn₆Zr₁ catalyst, which reduced the reduction temperature of the catalyst. In summary, zirconium doping successfully improved the NH₃-SCR performance of MnO_x.

Mn_xZr₁ series catalysts were prepared by a coprecipitation method.     

Fe2O3 enhanced high-temperature arsenic resistance of CeO2–La2O3/TiO2 catalyst for selective catalytic reduction of NOx with NH3

High-temperature arsenic resistance catalysts of CeLa_0.5Fe_x/Ti (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) series were prepared and measured under a simulation condition of arsenic poisoning. The as-prepared catalysts were characterized by XRD, SEM, TEM, and XPS. The specific surface area and pore size of the catalysts were measured. At x = 0.2, the catalyst shows the best arsenic resistance and catalytic performance. The active temperature range of the CeLa_0.5Fe_0.2/Ti catalyst is 345–520 °C when the gas hourly space velocity is up to 225 000 mL g⁻¹ h⁻¹. Compared with commercial vanadium-based catalysts, CeLa_0.5Fe_0.2/Ti shows much better catalytic performance. The introduction of Fe will improve the dispersion of CeO₂ and increase the concentration of Ce³⁺ and unsaturated active oxygen on the surface. The NH₃-TPD and H₂-TPR results show that the CeLa_0.5Fe_0.2/Ti catalyst has more acidic sites and more excellent redox performance than CeLa_0.5Fe₀/Ti. The CeLa_0.5Fe_0.2/Ti catalyst might have application prospects in the field of selective catalytic reduction of NO_x with NH₃.

The NO conversion of the CeLa_0.5Fe_0.2/Ti is obviously better than that of the commercial vanadium-based catalyst with regard to arsenic resistance and it has good N₂ selectivity, and good SO₂ resistance.     

Ce regulated surface properties of Mn/SAPO-34 for improved NH3-SCR at low temperature

Ce modified MnO_x/SAPO-34 was prepared and investigated for low-temperature selective catalytic reduction of NO_x with ammonia (NH₃-SCR). The 0.3Ce–Mn/SAPO-34 catalyst had nearly 95% NO conversion at 200–350 °C at a space velocity of 10 000 h⁻¹. Microporous SAPO-34 as the support provided the catalyst with increased hydrothermal stability. XPS and H₂-TPR results proved that the Mn⁴⁺ and O_α content increased after incorporation of Ce, this promoted the conversion of NO at low temperature via a ‘fast SCR’ route. NH₃-TPD measurements combined oxidation experiments of NO, NH₃ indicated the reduction of both the surface acidity and the amount of acid sites, which effectively decreased the NH₃ oxditaion to NO or N₂O at elevated temperature and promoted the catalytic selectivity for nitrogen. A redox cycle between manganese oxide and Ce was assumed for the active oxygen transfer and facilitated the catalyst durability.

Ce modified MnO_x/SAPO-34 was prepared and investigated for low-temperature selective catalytic reduction of NO_x with ammonia (NH₃-SCR).     

Ultrasonic-assisted preparation of highly active Co3O4/MCM-41 adsorbent and its desulfurization performance for low H2S concentration gas

Co₃O₄/MCM-41 adsorbents were successfully prepared by ultrasonic assisted impregnation (UAI) and traditional mechanical stirring impregnation (TMI) technologies and characterized by X-ray diffraction (XRD), N₂ adsorption desorption, Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry-differential thermal analysis (TG-DTA). The H₂S removal performances for a simulated low H₂S concentration gas were investigated in a fixed-bed. The effect of preparation and adsorption conditions on the H₂S removal over Co₃O₄/MCM-41 were systematically examined. The results showed that UAI promotes more and well defined highly dispersed active Co₃O₄ phase on MCM-41. As compared to the Co₃O₄/MCM-41-T prepared via TMI, the saturated H₂S capacity of Co₃O₄/MCM-41-U prepared via UAI improved by 33.2%. The desulfurization performance of adsorbents decreased in the order of Co₃O₄/MCM-41-U > Co₃O₄/MCM-41-T > MCM-41. The Co₃O₄/MCM-41-U prepared using Co(NO₃)₂ concentration of 10%, ultrasonic time of 2 h, calcination temperature of 550 °C and calcination time of 3 h exhibited the best H₂S removal efficiency. At adsorption temperature of 25 °C with model gas flowrate of 20 mL min⁻¹, the breakthrough time of Co₃O₄/MCM-41-U was 10 min, and the saturated H₂S capacity and H₂S removal rate was 52.6 mg g⁻¹ and 47.8%, respectively.

Co₃O₄/MCM-41 adsorbent with high surface area and more active sites was successfully prepared by ultrasonic assisted impregnation (UAI) technology and it has been found that the sulfur capacity was improved by 33.2% because of ultrasonication.     

Solution combustion derived oxygen vacancy-rich Co3O4 catalysts for catalytic formaldehyde oxidation at room temperature

Fabricating abundant oxygen vacancies is crucial for non-noble metal oxides to catalyze formaldehyde (HCHO) oxidation at room temperature. Here, a simple one-pot preparation method via solution combustion was found to produce oxygen vacancy-rich Co₃O₄ catalysts, avoiding delicate defect engineering. The catalyst was evaluated to result in 52% HCHO conversion in a dynamic flow reaction with ∼6 ppm HCHO, which was higher as compared to some other Co₃O₄ catalysts prepared in three methods of sol–gel, deposition precipitation and thermal decomposition. The optimal catalyst also exhibited high durability with steady HCHO conversion (∼47%) for more than 50 h. The catalyst characterizations revealed that the explosive solution combustion brought out two particular features of Co₃O₄, namely, the porous network structure with nano-holes and the abundant oxygen vacancies. The latter was demonstrated to increase the reactive oxygen species and to improve the reducibility and the oxygen transport capacity of Co₃O₄. The two features and the derived properties are beneficial to the activity and durability of Co₃O₄. The solution combustion method can serve as a simple and feasible way to fabricate abundant oxygen vacancies to provide room-temperature activity of Co₃O₄ for HCHO elimination at room temperature.

The rich oxygen vacancies in porous Co₃O₄ were generated in solution combustion, offering high room-temperature activity for formaldehyde oxidation.