Broad Operation Temperature Window Research Articles

Ni-Ce-Ti as a superior catalyst for the selective catalytic reduction of NOx with NH3

A novel Ni-Ce-Ti mixed oxide catalyst prepared by the hydrothermal method has been developed for the selective catalytic reduction of NOx by NH3. It was found that Ni-Ce-Ti catalyst showed high NH3-SCR activity, excellent N2 selectivity with broad operation temperature window. Based on the catalyst characterization, the redox cycle (Ni3++Ce3+↔Ni2++Ce4+), the amorphous structure and more surface defects over Ni-Ce-Ti catalyst are responsible for the high catalytic deNOx performance. In situ DRIFT experiments demonstrated that the synergetic effect between Ni and Ce contributes to the formation of reactive NH3 on Lewis acid sites and monodentate nitrate, thus facilitating the NH3-SCR reaction to proceed. The present Ni-Ce-Ti catalyst has great potential for the practical removal of NOx.

Optimizing Magnetocaloric Properties of Heusler-Type Magnetic Shape Memory Alloys by Tuning Magnetostructural Transformation Parameters

Heusler-type magnetic shape memory alloys show a magnetostructural transformation from the low-magnetization phase to the high-magnetization phase upon the application of external magnetic fields. As a result, these alloys exhibit fascinating multifunctional properties, such as magnetic shape memory effect, magnetocaloric effect, magnetoresistance, and magnetic superelasticity. All these functional properties are intimately related to the coupling of the structural and magnetic transitions. Therefore, deliberate tuning of the magnetostructural transformation parameters is essential for obtaining optimal multifunctional properties. Here, we show that by tuning the magnetostructural transformation parameters, we are able to achieve a variety of novel magnetocaloric properties with different application potentials: (1) large magnetic entropy change of 31.9 J kg−1 K−1 under a magnetic field of 5 T; (2) giant effective magnetic refrigeration capacity (251 J kg−1) with a broad operating temperature window (33 K) under a magnetic field of 5 T; (3) large reversible field-induced entropy change (about 15 J kg−1 K−1) and large reversible effective magnetic refrigeration capacity (77 J kg−1) under a magnetic field of 5 T. The balanced tuning of magnetostructural transformation parameters of magnetic shape memory alloys may provide an instructive reference to the shape memory and magnetic refrigeration communities.

Large room-temperature rotating magnetocaloric effect in NdCo4Al polycrystalline alloy

Abstract The magnetic refrigeration based on rotating magnetocaloric effect (MCE) is promising to build a simplified magnetic cooling system. Until now, most magnetic refrigerants for rotating MCE are single crystal and work at low temperature, which hinder the development of this refrigeration technology. In present paper, we report a large room-temperature rotating MCE in a magnetic-field-aligned NdCo4Al polycrystalline alloy. A large rotating magnetic entropy change of 1.3 J kg−1 K−1 under 10 kOe and a broad operating temperature window of 52 K are achieved. The origin of large rotating MCE in NdCo4Al polycrystalline alloy and its advantages for rotating magnetic refrigeration are discussed.

Novel holmium-modified Fe-Mn/TiO2 catalysts with a broad temperature window and high sulfur dioxide tolerance for low-temperature SCR

Novel highly-efficient low-temperature SCR catalysts were developed through modifying Fe-Mn/TiO2 catalyst with holmium (Ho). It was found that Ho/Ti=0.1 was the optimal molar ratio for the amount of Ho addition. With this ratio, 85% NOx conversion was obtained at 60°C and the catalytic performance enhanced to 90% at 120°C. The optimal catalyst presented a broad operating temperature window in the range of 60–200°C and exhibited superior sulfur-poisoning resistance, while the further increase of the doped Ho did not have a positive effect on the catalytic performance and structural properties.

Study of magnetic entropy and heat capacity in ferrimagnetic Fe3Se4 nanorods

Change in the magnetic entropy and specific heat capacity in Fe3Se4 nanorods synthesized by a wet-chemical method in a broad temperature (215–340 K) and magnetic field range (0–60 k Oe) was studied. The isothermal magnetic entropy change (ΔSM) is estimated by an indirect method from the isothermal magnetization curves measured in this temperature range. of −46 × 10−2 J kg−1 · K−1 was obtained at ~317 K when the field was changed from 0 to 60 kOe. The maximum in the isothermal magnetic entropy change (ΔSM) is observed in close proximity to TC (~323 K), which is linked to the order–disorder transition. The nature of this transition was analyzed by universal curve behavior. The temperature and magnetic field dependence of specific heat capacity was studied and analyzed to estimate the adiabatic temperature change (ΔTad). The magnetic entropy change of Fe3Se4 nanoparticles is found to be comparable with similar ferrite and manganite nanoparticle systems and a broad operating temperature window of ~30 K was observed around room temperature.

Large reversible magnetocaloric effect in a Ni-Co-Mn-In magnetic shape memory alloy

Reversibility of the magnetocaloric effect in materials with first-order magnetostructural transformation is of vital significance for practical magnetic refrigeration applications. Here, we report a large reversible magnetocaloric effect in a Ni49.8Co1.2Mn33.5In15.5 magnetic shape memory alloy. A large reversible magnetic entropy change of 14.6 J/(kg K) and a broad operating temperature window of 18 K under 5 T were simultaneously achieved, correlated with the low thermal hysteresis (∼8 K) and large magnetic-field-induced shift of transformation temperatures (4.9 K/T) that lead to a narrow magnetic hysteresis (1.1 T) and small average magnetic hysteresis loss (48.4 J/kg under 5 T) as well. Furthermore, a large reversible effective refrigeration capacity (76.6 J/kg under 5 T) was obtained, as a result of the large reversible magnetic entropy change, broad operating temperature window, and small magnetic hysteresis loss. The large reversible magnetic entropy change and large reversible effective refrigeration capacity are important for improving the magnetocaloric performance, and the small magnetic hysteresis loss is beneficial to reducing energy dissipation during magnetic field cycle in potential applications.

Impacts of niobia loading on active sites and surface acidity in NbOx/CeO2–ZrO2 NH3–SCR catalysts

A series of NbOx/Ce0.75Zr0.25O2 catalysts for the selective catalytic reduction of NO with ammonia (NH3–SCR) were synthesized using a wetness impregnation method. The effect of niobia loading was studied in relation to the active sites and surface acidity. NH3/NO oxidation, X-ray diffraction, Infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, O2/NH3 temperature-programmed desorption, and diffuse reflectance infrared Fourier transformed spectroscopy experiments were performed to correlate the catalyst structure and surface properties to catalytic performance after Nb2O5 modification. The catalyst with 15wt.% Nb2O5 loading showed high NH3–SCR activity and nearly 100% N2 selectivity within a broad operation temperature window (190–460°C) at a high space velocity (300,000h−1). On this catalyst, Nbn+ was mainly distributed in the form of typical monomeric and polymeric NbOx species, and was partially incorporated into the Ce0.75Zr0.25O2 lattice at the Nbn+OCen+ (Zrn+) interface. The electron redistribution effect arising from the occupation of cerium sites by Nbn+ ions promoted the formation of Ce3+ ions, oxygen vacancies and active oxygen species. This interaction was closely associated with the distribution of NbOx species which varied with niobia loading. NbOx themselves were acid sites and by attracting electrons they enhanced Lewis acid sites on CZ surface, which promoted the adsorption of NH3 and inhibited the unselective oxidation of NH3 to NOx. The increased amounts of active oxygen species over NbCZ catalysts promoted the adsorptive oxidation of NH3 to NH2 and NO to NO3− at low temperatures, and thus facilitated the reaction of ads-NH3 and ads-NO3−/NO2− species. This effect as well as the increased amount of acid sites led to good NH3–SCR performance of Nb15CZ in a wide temperature range.

Mechanism of the selective catalytic reduction of NO x with NH3 over W-doped Fe/TiO2 catalyst

The W-doped Fe/TiO2 catalyst prepared by an impregnation method exhibited a good NH3-selective catalytic reduction(SCR) activity and N2 selectivity with broad operation temperature window. The interaction between Fe and W could increase the amount of surface chemisorbed oxygen, and thus enhances the low temperature SCR activity by facilitating the fast SCR of 2NH3+NO+NO2→2N2+3H2O. The NH3-SCR reaction mechanism over the W-Fe/TiO2 was fully investigated via in situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS). In the low temperature range( 250 °C), the reactive surface species were mainly NH2, and the SCR mainly followed the Eley-Rideal mechanism, during which the formation of NH2NO intermediate species after H-abstraction of NH3 was the rate-determining step.

Novel promoting effects of cerium on the activities of NOx reduction by NH3 over TiO2-SiO2-WO3 monolith catalysts

A series of catalysts were prepared by doping different loadings of CeO2 over TiO2-SiO2-WO3 and used for the selective catalytic reduction of NOx by NH3. The experimental results showed that the selective catalytic reduction (SCR) performance and SO2-resistant ability of TiO2-SiO2-WO3 were greatly enhanced by the introduction of cerium. The catalyst containing 10% CeO2 showed the highest NO conversion in a wide temperature range and good N2 selectivity with broad operation temperature window at the gas hourly space velocity (GHSV) of 30000 h−1, which was a very promising catalyst for NOx abatement from diesel engine exhaust. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), N2 adsorption-desorption (BET) and X-ray photoelectron spectroscopy (XPS). The characterization results showed that the bigger pore radius, higher surface atomic concentration and dispersion of Ce and the abundant adsorbed oxygen on the surface of catalyst contributed to the best NH3-SCR performance of CeO2/TiO2-SiO2-WO3 catalyst containing 10% CeO2.

Novel Mn-Ce-Ti mixed-oxide catalyst for the selective catalytic reduction of NOx with NH₃.

Mn-Ce-Ti mixed-oxide catalyst prepared by the hydrothermal method was investigated for the selective catalytic reduction (SCR) of NOx with NH3 in the presence of oxygen. It was found that the environmentally benign Mn-Ce-Ti catalyst exhibited excellent NH3-SCR activity and strong resistance against H2O and SO2 with a broad operation temperature window, which is very competitive for the practical application in controlling the NOx emission from diesel engines. On the basis of the catalyst characterization, the dual redox cycles (Mn(4+) + Ce(3+) ↔ Mn(3+) + Ce(4+), Mn(4+) + Ti(3+) ↔ Mn(3+) + Ti(4+)) and the amorphous structure play key roles for the high catalytic deNOx performance. Diffuse reflectance infrared Fourier transform spectroscopy studies showed that the synergetic effect between Mn and Ce contributes to the formation of reactive intermediate species, thus promoting the NH3-SCR to proceed.

A Remarkable Catalyst Combination to Widen the Operating Temperature Window of the Selective Catalytic Reduction of NO by NH3

AbstractOn the basis of the idea of combining high selective catalytic reduction (SCR) activity, high N2 selectivity, and broad operating temperature window, we developed a combined catalyst process that was found to be a convenient way to design a highly efficient SCR process for NO with NH3. The single catalysts of MnOx–CeO2/TiO2 and V2O5–WO3/TiO2 as well as combined catalysts with different configurations were fully characterized by XRD, temperature‐programmed reduction of H2, and temperature‐programmed desorption of NO/O2. In addition, they were tested for the oxidation of NO or NH3 as well as the SCR of NO with NH3. The correlations between combining configurations and SCR activity results were also revealed. Furthermore, fundamental evidences were given for the rational design of the process and its efficiency maximization (assembly order and catalytic bed volume). An adequate configuration, with MnOx–CeO2/TiO2 and V2O5–WO3/TiO2 active materials, ensures an excellent SCR performance (NO conversion >85 %, N2 yield >70 %, and decreased N2O production) over a wide operating temperature window (from 150 to 400 °C).

Giant magnetic refrigeration capacity near room temperature in Ni40Co10Mn40Sn10 multifunctional alloy

We report a giant effective magnetic refrigeration capacity in a Ni40Co10Mn40Sn10 multifunctional alloy. With a large magnetization difference between austenite and martensite, this alloy shows a strong magnetic field dependence of transformation temperatures. Complete magnetic-field-induced structural transformation and a considerable magnetic entropy change are observed in a broad operating temperature window of 33 K near room temperature. Consequently, an effective magnetic refrigeration capacity of 251 J/kg for 5 T is achieved, which is the largest value for Ni-Mn-based Heusler alloys and comparable to that of the high-performance Gd-Si-Ge and La-Fe-Si magnetocaloric materials. Incorporating the advantages of low cost and non-toxicity, this alloy shows very promising prospects for room-temperature magnetic refrigeration.

Catalytic performance of acidic zirconium-based composite oxides monolithic catalyst on selective catalytic reduction of NOx with NH3

A series of monolithic acidic zirconium-based composite oxide catalyst (Ce–ZrTiSiWOx) were prepared by different introduction methods and loading contents of CeO2 for selective catalytic reduction (SCR) of NOx with ammonia. In this work, a acidic zirconium-based composite oxide (10wt.% CeO2/ZrTiSiWOx) catalyst prepared only by impregnation method presented good NH3-SCR activity and high N2 selectivity in a broad operation temperature window, comparative strong tolerance of gas hourly space velocities (GHSV), water, sulfur and hydrothermal aging. Compared with V2O5/TiSiWOx and Fe-ZSM-5 catalysts, the CeO2/ZrTiSiWOx catalyst showed a better NH3-SCR performance and higher thermal aged performance. More than 80% NOx could be removed in the temperature range of 277–545°C under GHSV of 30,000h−1 over the monolithic 10wt.% CeO2/ZrTiSiWOx catalyst. More surface atomic concentration of Ce, strong reducible ability and the maximum acid amount are important reasons for the high NH3-SCR activity of the CeO2/ZrTiSiWOx catalyst.

A superior catalyst with dual redox cycles for the selective reduction of NOx by ammonia

An environmentally benign Cu-Ce-Ti oxide catalyst exhibited excellent NH3-SCR activity, high N2 selectivity and strong resistance against H2O and SO2 with a broad operation temperature window. The dual redox cycles (Cu(2+) + Ce(3+) ↔ Cu(+) + Ce(4+), Cu(2+) + Ti(3+) ↔ Cu(+) + Ti(4+)) play key roles for the superior catalytic deNOx performance.

A superior Ce-W-Ti mixed oxide catalyst for the selective catalytic reduction of NOx with NH3

A superior Ce-W-Ti mixed oxide catalyst prepared by a facile homogeneous precipitation method showed excellent NH3-SCR activity and 100% N2 selectivity with broad operation temperature window and extremely high resistance to space velocity, which is a very promising catalyst for NOx abatement from diesel engine exhaust. The excellent catalytic performance is associated with the highly dispersed active Ce and promotive W species on TiO2. The introduction of W species could increase the amount of active sites, oxygen vacancies, and Brønsted and Lewis acid sites over the catalyst, which is also beneficial to improve the low temperature activity by facilitating “fast SCR” reaction and enhance both of the high temperature activity and N2 selectivity simultaneously by inhibiting the unselective oxidation of NH3 at high temperatures.

An environmentally-benign CeO2-TiO2 catalyst for the selective catalytic reduction of NOx with NH3 in simulated diesel exhaust

A Ce-Ti based (CeO2-TiO2) catalyst prepared by an optimized homogeneous precipitation method showed excellent NH3-SCR activity, high N2 selectivity, broad operation temperature window, and high resistance to space velocity (even under a high gas hourly space velocity (GHSV) of 500,000h−1). Compared with V2O5-WO3/TiO2 and Fe-ZSM-5 catalysts, the CeO2-TiO2 catalyst showed better catalytic performance for NH3-SCR. Under a more realistic condition of simulated diesel engine exhaust, the monolith catalyst of CeO2-TiO2 showed over 90% NOx conversion from 250 to 450°C under a GHSV of 20,000h−1 in the presence of H2O, CO2, and C3H6. The high dispersion of active CeO2 on TiO2 in the process of homogenous precipitation and the synergistic effects between CeO2 and TiO2 in CeO2-TiO2 are important reasons for the high NH3-SCR activity.