Rough and Porous Micropebbles of CeCu2Si2 for Energy Storage Applications

Supercapacitors have attracted considerable attention due to their advantages, including being lightweight and having rapid charge-discharge, a good rate capability, and high cyclic stability. Electrodes are one of the most important factors influencing the performance of supercapacitors. Herein, a three-dimensional network of rough and porous micropebbles of CeCu2Si2 has been prepared using a one-step procedure and tested for the first time as a supercapacitor electrode. The synthesized material was extensively characterized in a three-electrode configuration using different electrochemical techniques, such as cyclic voltammetry (CV), galvanostatic charge and discharge (GCD) tests, and electrochemical impedance spectroscopy (EIS). CeCu2Si2 shows rather high mass-capacitance values: 278 F/g at 1 A/g and 295 F/g at 10 mV/s. Moreover, the material exhibits remarkable long-term stability: 98% of the initial capacitance was retained after 20,000 cycles at 10 A/g and the Coulombic efficiency remains equal to 100% at the end of the cycles.

Hollow @CuMgAl double layered hydrotalcites and mixed oxides with tunable textural and structural properties, and thus enhanced NH3-NOx-SCR activity

Well-organized, spherical, mesoporous hollow @CuMgAl-LDHs (layered double hydroxides) are prepared by the controlled removal of the SiO₂ from SiO₂@CuMgAl-LDH core-shell hybrids that in turn are synthesized via a bottom-up strategy. The materials are prepared with various Cu/Mg molar ratios (Cu/Mg = 0.05-0.50) while keeping the ratio of Cu and Mg constant, (Cu + Mg)/Al = 2. The effect of Cu doping and the silica core removal process (conducted for 4 h at 30 °C using 1 M NaOH) on the chemical composition, morphology, structure, texture and reducibility of the resulting materials are described. @CuMgAl-MOs (mixed oxides) obtained by thermal treatment of the @CuMgAl-LDHs are active and selective catalysts for the selective catalytic reduction of NO_x using ammonia, and effectively operate at low temperatures. The N₂ yield increases with increased Cu content in the CuMgAl shell, which is associated with the easier reducibility of the Cu species incorporated into the MgAl matrix. @CuMgAl-MOs show better catalytic performance than bulk CuMgAl MOs.

Fabrication of wide temperature FexCe1-xVO4 modified TiO2-graphene catalyst with excellent NH3-SCR performance and strong SO2/H2O tolerance

Selective catalytic reduction of NO with NH₃ (NH₃-SCR) is one of the most common technique for elimination of NO_x. The promotional effect of Fe additive on the NH₃-SCR activity of the CeVO₄/TiO₂-graphene (GE) is systematically studied. The results exhibited that the low-temperature NO_x conversion could be enhanced dramatically via the addition of Fe and Fe_0.5Ce_0.5VO₄/TiO₂-GE displayed the highest conversion of NO_x in the wide temperature window (200-400 °C). It is because that Fe³⁺ + Ce³⁺ ↔ Fe²⁺ + Ce⁴⁺ facilitated the oxidization of NO to NO₂ at low temperature and led to the "Fast SCR," thereby raising the SCR performance. What is more, the introduction of Fe enhanced redox ability, the surface relative percentage of Ce³⁺, V⁵⁺ and the chemical adsorbed oxygen. Furthermore, the high surface concentration of Ce³⁺ species can produce more active oxygen and leads to the "Fast SCR" reaction. In addition, the Fe_0.5Ce_0.5VO₄/TiO₂-GE catalyst showed excellent H₂O/SO₂ tolerance, which may be due to the decomposition of ammonium bisulphite under high temperature and the hydrophobicity of graphene. What is more, it displayed outstanding the stability. This work would provide theoretical reference for the practical application of NO_x abatement via NH₃-SCR.

Fe2O3 enhanced high-temperature arsenic resistance of CeO2-La2O3/TiO2 catalyst for selective catalytic reduction of NO x 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.

FeVO4-supported Mn–Ce oxides for the low-temperature selective catalytic reduction of NOx by NH3

Iron vanadate (FeVO4) nanorods are used as a carrier to support manganese (Mn) and cerium (Ce) oxides for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with NH3 for the first time.

Recent advances in layered double hydroxides (LDHs) derived catalysts for selective catalytic reduction of NOx with NH3

In recent years, layered double hydroxides (LDHs) derived metal oxides as highly efficient catalysts for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) have attracted great attention. The high dispersibility and interchangeability of cations within the brucite-like layers make LDHs an indispensable branch of catalytic materials. With the increasingly stringent and ultra-low emission regulations, there is an urgent need for highly efficient and stable low-medium temperature denitration catalysts in markets. In this contribution, we have critically summarized the recent research progress in the LDHs derived NH₃-SCR catalysts, including their ability for NO_x removal, N₂ selectivity, active temperature window, stability and resistance to poisoning. The advantages and defects of various types of LDHs-derived catalysts are comparatively summarized, and the corresponding modification strategies are discussed. In addition, considering the importance of the catalyst's resistance to poisoning in practical applications, we discuss the poisoning mechanism of each component in flue gases, and provide the corresponding strategies to improve the poisoning resistance of catalysts. Finally, from the perspective of practical applications and operation cost, the regeneration measures of catalysts after poisoning is also discussed. We hope that this work can give timely technical guidance and valuable insights for the applications of LDHs materials in the field of NO_x control.

A study on the selective catalytic reduction of NO x by ammonia on sulphated iron-based catalysts

A series of sulphated iron-based catalysts was prepared via an impregnation method by changing the loading content of Fe³⁺ and SO₄²⁻ on ZrO₂, and their performance in the selective catalytic reduction (SCR) of NO_x by ammonia was investigated. The NO_x conversion exhibited large differences among the sulphated iron-based catalysts. To explore the synergistic mechanism of iron and sulphates, XRD, BET, H₂-TPR, XPS, TPD and in situ DRIFTS were used to characterize the catalysts, and it was found that among all the catalysts, the NO_x conversion by Fe₂SZr was greater than 90% at 350–450 °C. The results indicated that the interaction between Fe³⁺ and SO₄²⁻ can have an effect on the redox ability, acid sites, and adsorption of NO_x and NH₃. With an increase in the content of Fe³⁺, the redox activity of the catalyst and the adsorption of ammonia improved at medium and low temperatures. However, at higher temperatures, an increase in Fe³⁺ led to a decrease in the conversion of NO_x due to the enhanced oxidation of NH₃. At medium and low temperatures, an increase in the content of SO₄²⁻ decreased the concentration of Fe³⁺ on the surface of the catalyst and inhibited the adsorption of NO_x and NH₃. The addition of SO₄²⁻ reduced the redox activity of the catalyst and inhibited the oxidation reaction of NH₃, which follows the Eley–Rideal mechanism at high temperatures, further enhancing the SCR activity of the Fe_xS_yZr catalyst.

The roles of Fe³⁺ and SO₄²⁻ are different at low and high temperatures due to their interaction. It is the appropriate contents of Fe³⁺ and SO₄²⁻ that can result in high NH₃-SCR activity at varying temperatures.

Modification of composite catalytic material CumVnOx@CeO2 core-shell nanorods with tungsten for NH3-SCR

Novel composite material CumVnOx-NF@Ce-MOF nanorods with a core-shell structure were successfully fabricated by the in situ growth of Ce-MOF on electrospun copper vanadate precursor nanofibers. Following calcination at 500, 600 and 700 °C, Cu2V2O7@CeO2, Cu3(VO4)2@CeO2 and Cu11O2(VO4)6@CeO2, respectively, were obtained. The CeO2 shell not only protected the copper vanadate nanofibers from breaking apart during the calcination process, but also induced an interaction between Ce, Cu and V species, which resulted in an excellent redox capacity. This revealed its potential as a catalyst for the selective catalytic reduction of nitrogen oxides with NH3 (NH3-SCR). Further surface modulation was accomplished by WOx anchoring on the shell of CumVnOx@CeO2. According to a series of characterizations, the crystallinity of surface ceria on CumVnOy@CeO2-WOx was apparently reduced and the amount of acid on its surface was also significantly increased. In addition, different calcination temperatures also had nonnegligible effects on the amount of surface acid as well as the redox capacity of the composite catalytic material CumVnOy@CeO2-WOx. With the largest total quantity of acid sites as well as a suitable balance between acidity and reducing ability, the Cu3(VO4)2@CeO2-WOx calcined at 600 °C exhibited satisfactory catalytic performance in the NH3-SCR process, and the NO conversion could remain above 90% at 230-380 °C.

A superior Fe-V-Ti catalyst with high activity and SO2 resistance for the selective catalytic reduction of NOx with NH3

A series of Fe-V-Ti oxide catalysts were prepared by a co-precipitation method, among which the Fe_0.1V_0.1TiO_x catalyst showed the optimal NH₃-SCR performance and excellent SO₂ resistance. Fe_0.1V_0.1TiO_x achieved > 90% NO_x conversion at 225-450 °C under a GHSV of 200,000 h^-1. When introducing SO₂ and H₂O to the SCR reaction for 24 h, the NO_x conversion maintained a level above 93% at 250 °C. The Raman and Mössbauer spectra showed that FeVO₄ and Fe₂O₃ coexisted on the surface of TiO₂. In Fe-V-Ti catalysts, the charge interaction between Fe₂O₃ and FeVO₄ as well as the electronic inductive effect between Fe and V species resulted in the improvement of SCR activity and N₂ selectivity at high temperatures. The NH₃-SCR process on the Fe_0.1V_0.1TiO_x catalyst mainly followed the Eley-Rideal (E-R) reaction mechanism with gaseous NO reacting with adsorbed NH₃ adsorbed species.