Carbon cloth supporting spinel CuMn0.5Co2O4 nanoneedles with the regulated electronic structure by multiple metal elements as catalysts for efficient oxygen evolution reaction

Developing transition metal oxide catalysts to replace the noble metal oxide catalysts for efficient oxygen evolution reaction (OER) is essential to promote the practical application of water splitting. Herein, we designed and constructed the carbon cloth (CC) supporting spinel CuMn_0.5Co₂O₄ nanoneedles with regulated electronic structure by multiple metal elements with variable chemical valences in the spinel CuMn_0.5Co₂O₄. The carbon cloth not only provided good conductivity for the catalytic reaction but also supported the well-standing spinel CuMn_0.5Co₂O₄ nanoneedles arrays with a large special surface area. Meanwhile, the well-standing nanoneedles arrays and mesoporous structure of CuMn_0.5Co₂O₄ nanoneedles enhanced their wettability and facilitated access for electrolyte to electrochemical catalysis. Besides, the regulated electronic structure and generated oxygen vacancies of CuMn_0.5Co₂O₄/CC by multiple metal elements improved the intrinsic catalytic activity and the durability of OER activity. Profiting from these merits, the CuMn_0.5Co₂O₄/CC electrode exhibited superior OER activity with an ultralow overpotential of 189 mV at the current density of 10 mA⋅cm^-2 and a smaller Tafel slope of 64.1 mV⋅dec^-1, which was competitive with the noble metal oxides electrode. And the CuMn_0.5Co₂O₄/CC electrode also exhibited long-term durability for OER with 95.3% of current retention after 1000 cycles. Therefore, the competitive OER activity and excellent cycling durability suggested that the CuMn_0.5Co₂O₄/CC electrode is a potential candidate catalyst for efficient OER.

Diesel particulate filter regeneration mechanism of modern automobile engines and methods of reducing PM emissions: a review

Diesel particulate filter (DPF) is considered as an effective method to control particulate matter (PM) emissions from diesel engines, which is included in the mandatory installation list by more and more national/regional laws and regulations, such as CHINA VI, Euro VI, and EPA Tier3. Due to the limited capacity of DPF to contain PM, the manufacturer introduced a method of treating deposited PM by oxidation, which is called regeneration. This paper comprehensively summarizes the most advanced regeneration technology, including filter structure, new catalyst formula, accurate soot prediction, safe and reliable regeneration strategy, uncontrolled regeneration and its control methods. In addition, due to the change of working conditions in the regeneration process, the additional emissions during regeneration are discussed in this paper. The DPF is not only the aftertreatment device but also can be combined with diesel oxidation catalyst (DOC), selective catalytic reduction (SCR) and exhaust recirculation (EGR). In addition, the impact of DPF modification on the original system of some old models has been reasonably discussed in order to achieve emission targets.

A Highly Stable and Sustainable Low-Temperature Selective Absorber: Structural and Ageing Characterisation

Solar absorbers in a three-layer configuration have been prepared by dip-coating onto aluminium substrates. They are constituted by two spinel layers with one silica layer on the top and values of solar absorptance above 0.950 and thermal emittance below 0.04 were obtained. The effects of using different sintering conditions of the upper silica layer on the optical behaviour and durability tests have been studied. Results obtained in accelerated ageing methods, such as thermal stability tests and condensation tests, clearly show that the proposed selective absorber exhibits excellent thermal stability and very good humidity resistance. The results show that the protective action is due not only to the silica layer but also to the alumina layer produced during the absorber preparation. The phase composition of the individual layers was independently confirmed using X-ray diffraction and corroborated by X-ray Photoelectron Spectroscopy. Spinel-like phases were obtained in both the first and second layers. The ageing study shows that the three-layer configuration proposed has a very high potential, in terms of both durability and optical behaviour, for solar thermal low-temperature applications.

Preparation of Cordierite Monolith Catalysts with the Coating of K-Modified Spinel MnCo2O4 Oxide and Their Catalytic Performances for Soot Combustion

Diesel engines are important for heavy-duty vehicles. However, particulate matter (PM) released from diesel exhaust should be eliminated. Nowadays, catalytic diesel particulate filters (CDPF) are recognized as a promising technology. In this work, a series of monolith Mn1−nKnCo2O4 catalysts were prepared by the simple citric acid method. The as-prepared catalysts displayed good catalytic performance for soot combustion and the Mn0.7K0.3Co2O4 catalyst gave the best catalytic performance among all the prepared samples. The T10 and Tm of Mn0.7K0.3Co2O4-HC catalyst for soot combustion are 310 and 439 °C, respectively. The physical and chemical properties of catalysts were characterized by means of SEM, XPS, H2-TPR, Raman and other techniques. The characterization results indicate that K substitution is favorable for the formation of oxygen vacancies, enhancing the mobility of active oxygen species, and improving the redox properties and so on. In-situ Raman results prove that the strength of Co-O bonds in the catalysts became weak during the reaction at high temperatures. In addition, SEM and ultrasonic test results show that the peeling rate of the coat-layer is less than 5%. The as-prepared catalysts can be taken as one kind of candidate catalyst for promising application in soot combustion because of its facile synthesis, low cost and high catalytic activity.

Study of physical properties of a ferrimagnetic spinel Cu1.5Mn1.5O4: spin dynamics, magnetocaloric effect and critical behavior

The present work reports a detailed study of the spin dynamics, magnetocaloric effect and critical behaviour near the magnetic phase transition temperature, of a ferrimagnetic spinel Cu_1.5Mn_1.5O₄. The dynamic magnetic properties investigated using frequency-dependent ac magnetic susceptibility fitted using different phenomenological models such as Neel-Arrhenius, Vogel-Fulcher and power law, strongly indicate the presence of a cluster-glass-like behavior of Cu_1.5Mn_1.5O₄ at 40 K. The magnetization data have revealed that our compound displays an occurrence of second-order paramagnetic (PM) to ferrimagnetic (FIM) phase transition at the Curie temperature T _C = 80 K as the temperature decrease. In addition, the magnetic entropy change (ΔS _M) was calculated using two different methods: Maxwell relations and Landau theory. An acceptable agreement was found between both sets of data, which proves the importance of both electron interaction and magnetoelastic coupling in the magnetocaloric effect (MCE) properties of Cu_1.5Mn_1.5O₄. The relative cooling power (RCP) reaches 180.13 (J kg^-1) for an applied field at 5 T, making our compound an effective candidate for magnetic refrigeration applications. The critical exponents β, γ and δ as well as transition temperature T _C were extracted from various techniques indicating that the magnetic interaction in our sample follows the 3D-Ising model. The validity of the critical exponents is confirmed by applying the Windom scaling hypothesis.

Fabrication of Cu1.5Mn1.5O4 Nanoparticles Using One Step Self-Assembling Route to Enhance Energy Consumption

The preparation of copper manganite (hopcalite, Cu1.5Mn1.5O4), as a single phase, was achieved by using a sustainable method of green synthesis. This method is based on the replacement of the conventional “brute force” ceramic preparation by the recent “soft force” green synthesis via the egg white assisted one-step method. In other words, we present a facile and rapid methodology to prepare the nanocrystalline Cu1.5Mn1.5O4 spinel as a single phase, compared to our previous work using ceramic and glycine-assisted combustion methods. The as-synthesized copper manganite was characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR), energy-dispersive spectroscopy (EDS), and scanning electron microscope (SEM). We used a vibrating sample magnetometer to determine the magnetic properties of the prepared sample (VSM). XRD, FTIR, SEM, EDS and transmittance electron micrograph (TEM) resulted in synthesis of a successful cubic spinel Cu1.5Mn1.5O4 system with a sponge crystal structure. The particles of the prepared materials are polycrystalline in their nature and the sizes ranged between 50 and 100 nm. The magnetic measurement demonstrated that the generated nanostructure has been found to exhibit ferromagnetism at room temperature with an optimum saturation magnetization value (0.2944 emu/g).

Efficient catalytic degradation of toluene at a readily prepared Mn-Cu catalyst: Catalytic performance and reaction pathway

Fabricating of economical transitional metal oxide-based materials with satisfied low-temperature catalytic performance and application perspective is still a challenge in deep degradation of VOCs. Here, Mn-Cu bimetallic oxides were facilely prepared by one-step hydrothermal-redox method, which displayed much higher catalytic activity in toluene oxidation than those synthesized by hydrolysis-driven redox-precipitation or co-precipitation approach. It is shown that the lattice defect and oxygen vacancy concentration over prepared materials can be tuned by controlling Cu/Mn molar ratio. Amongst, spinel structured MnCu_0.5 exhibited the highest catalytic activity, superior durability and water resistance in toluene total oxidation owing to abundant surface adsorbed oxygen species, excellent low-temperature reducibility, and high amounts of Cu⁺ and Mn³⁺. In detail, the reaction rate of MnCu_0.5 was over 9.0 times higher than that of MnCu_0.75, MnCu_0.75-P and MnCu_0.75-H₂O₂ at relative low temperature of 210 °C. The cyclic redox process with easier oxygen species mobility played a key role in the catalytic oxidation of toluene. Typical reaction intermediates as benzyl alcohol, benzaldehyde, benzene, phenol, and benzoquinone could be detected by PTR-MS, which further decomposed to acetone, ethanol, ketone, acetic acid, methanol, formaldehyde and acetaldehyde species by ring opening before total mineralization.

Structural, optical and dielectric properties of Cu1.5Mn1.5O4 spinel nanoparticles

In this study, a Cu_1.5Mn_1.5O₄ spinel was successfully synthesized by a sol–gel method at 500 °C for 5 h and characterized by different techniques. X-ray diffraction (XRD), Fourier transformation infrared (FTIR) spectroscopy and Raman spectroscopic analyses confirmed the formation of a spinel cubic structure with the Fd3̄m space group. The SEM proves that the grain size of our compound is of the order of 48 nm. Crystallite sizes determined from three estimates are closer to the grain size obtained from the SEM, indicating the single domain nature of the sample. The optical properties of UV-visible spectroscopy for our sample showed that the gap value is equal to 3.82 eV, making our compound a good candidate for optoelectronic applications. For electrical properties, impedance spectroscopy was performed at a frequency range of 40 ≤ frequency ≤ 10⁶ Hz. This suggested hoping conduction due to three theoretical models. The latter can be attributed to the correlated barrier hopping (CBH) model in region I, overlapping large polaron tunneling (OLPT) in region II and non-overlapping small polaron tunneling (NSPT) mechanism in region III. One dielectric relaxation is detected from the dielectric impedance and modulus, attributed to grain contributions. This behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance at different measuring temperatures.

In this study, a Cu_1.5Mn_1.5O₄ spinel was successfully synthesized by a sol–gel method at 500 °C for 5 h and characterized by different techniques.

Performance and Stability of Wet-Milled CoAl2O4, Ni/CoAl2O4, and Pt,Ni/CoAl2O4 for Soot Combustion

Low-energy wet milling was employed to activate commercial CoAl2O4 spinel and disperse mono- and multimetallic nanoparticles on its surface. This method yielded efficient Pt,Ni catalysts for soot oxidation in simulated diesel exhaust conditions. The characterization and activity results indicated that although Ni/CoAl2O4 was highly active, the presence of Pt was required to obtain a stable Ni(0.25 wt. %),Pt(0.75 wt. %)/CoAl2O4 catalyst under the operating conditions of diesel particulate filters, and that hot spots formation must be controlled to avoid the deactivation of the cobalt aluminate. Our work provides important insight for new design strategies to develop high-efficiency low-cost catalysts. Platinum-containing multimetallic nanostructures could efficiently reduce the amount of the costly, but to date non-replaceable, Pt noble metal for a large number of industrially important catalytic processes.

La2O2CO3-Induced phase composition oscillation in La–Cu mixed oxides during repeated catalytic soot combustion

La₂O₂CO₃-Induced phase composition oscillation between phase 1 (CuO + La₂O₂CO₃) and phase 2 (La₂CuO₄) in La–Cu mixed oxides during repeated catalytic soot combustion.

Reasons for the disintegration of microspherical precursor MnCO3 for soot combustion catalysts Ptδ+/MnOx

Facile Pt(NO₃)₂- or NH₃-treatment optimizes soot combustion catalyst MnO_x by disintegrating oversized microspheres and tuning the phase-composition and physiochemical properties.

Catalytic combustion of diesel soot over Fe and Ag-doped manganese oxides: role of heteroatoms in the catalytic performances

Fe/Ag-doped manganese oxides show promising catalytic activities in diesel soot combustion, which occurviamechanisms involving activated surface/lattice oxygen species.

Effects of sonication on co-precipitation synthesis and activity of copper manganese oxide catalyst to remove methane and sulphur dioxide gases

The utilisation of ultrasound in chemical preparation has been the focus of intense study in various fields, including materials science and engineering. This paper presents a novel method of synthesising the copper-manganese oxide (Hopcalite) catalyst that is used for the removal of volatile organic compounds and greenhouse gases like carbon monoxide. Several samples prepared under different conditions, with and without ultrasound, were subjected to a series of characterisation tests such as XRD, BET, FE-SEM, EDX, TPR-H₂, TGA and FT-IR in order to establish their chemical and physical properties. A series of catalytic tests using a micro-reactor were subsequently performed on the samples in order to substantiate the aforementioned properties by analysing their ability to oxidise compressed natural gas (CNG), containing methane and sulphur dioxide. Results showed that ultrasonic irradiation of the catalyst led to observable alterations in its morphology: surfaces of the particles were noticeably smoothed and an increased in amorphicity was detected. Furthermore, ultrasonic irradiation has shown to enhance the catalytic activity of Hopcalite, achieving a higher conversion of methane relative to non-sonicated samples. Varying the ultrasonic intensity also produced appreciable effects, whereby an increase in intensity results in a higher conversion rate. The catalyst sonicated at the highest intensity of 29.7W/cm² has a methane conversion rate of 13.5% at 400°C, which was the highest among all the samples tested.