Electrospun Ce-Mn oxide as an efficient catalyst for soot combustion: Ce-Mn synergy, soot-catalyst contact, and catalytic oxidation mechanism

Increasing the contact efficiency and improving the intrinsic activity are two effective strategies to obtain efficient catalysts for soot combustion. Herein, the electrospinning method is used to synthesize fiber-like Ce-Mn oxide with a strong synergistic effect. The slow combustion of PVP in precursors and highly soluble manganese acetate in spinning solution facilitates the formation of fibrous Ce-Mn oxides. The fluid simulation clearly indicates that the slender and uniform fibers provide more interwoven macropores to capture soot particles than the cubes and spheres do. Accordingly, electrospun Ce-Mn oxide exhibits better catalytic activity than reference catalysts, including Ce-Mn oxides by co-precipitation and sol-gel methods. The characterizations suggest that Mn³⁺ substitution into fluorite-type CeO₂ enhances the reducibility through the acceleration of Mn-Ce electron transfer, improves the lattice oxygen mobility by weakening the Ce-O bonds, and induces oxygen vacancies for the activation of O₂. The theoretical calculation reveals that the release of lattice oxygen becomes easy because of a low formation energy of oxygen vacancy, while the high reduction potential is beneficial for the activation of O₂ on Ce³⁺-Ov (oxygen vacancies). Due to above Ce-Mn synergy, the CeMnO_x-ES shows more active oxygen species and higher oxygen storage capacity than CeO₂-ES and MnO_x-ES. The theoretical calculation and experimental results suggest that the adsorbed O₂ is more active than lattice oxygen and the catalytic oxidation mainly follows the Langmuir-Hinshelwood mechanism. This study indicates that electrospinning is a novel method to obtain efficient Ce-Mn oxide.

Effect of oxygen vacancy and highly dispersed MnOx on soot combustion in cerium manganese catalyst

Cerium manganese bimetallic catalysts have become the focus of current research because of their excellent catalytic performance for soot combustion. Two series of cerium manganese catalysts (Na-free catalysts and Na-containing catalysts) were prepared by coprecipitation method and characterized using XRD, N₂ adsorption-desorption, SEM, Raman, XPS, H₂-TPR, O₂-TPD, Soot-TPR-MS and in situ IR. The effects of abundant oxygen vacancies and surface highly dispersed MnO_x on soot catalytic combustion of cerium manganese catalysts prepared by different precipitants were analyzed. The activity test results show that the active oxygen species released by a large number of oxygen vacancies in the cerium manganese catalyst are more favorable to the soot catalytic combustion than MnO_x which is highly dispersed on the surface of the catalyst and has good redox performance at low temperature. Because the catalytic effect of MnO_x on the surface of Na-free catalysts is more dependent on the contact condition between the catalyst and the soot, this phenomenon can be observed more easily under the loose contact condition than under the tight contact condition. The activity cycle test results show that these two series of catalysts show good stability and repeated use will hardly cause any deactivation of the catalysts.

Solvothermal synthesis of CeO2-ZrO2-M2O3 (M = La, Y, Bi) mixed oxide and their soot oxidation activity

CeO₂–ZrO₂-M₂O₃ (M = La, Y, Bi) mixed oxide has been prepared by a solvothermal synthesis method. The physico–chemical properties of the mixed oxide have been studied by X-ray powder diffraction (XRD), Raman spectroscopy, BET, X-ray photoelectron spectroscopy (XPS), TEM and temperature-programmed reduction (TPR), and the catalytic activity for soot oxidation has been studied by thermogravimetry (TG). La³⁺, Y³⁺ and Bi³⁺ exhibit positive effects on lowering the oxidation temperature of the soot. The XRD and Raman results showed formation of mixed oxides and TEM images suggested the nanosized nature of the particles. The benefit of yttrium or lanthana doping on the catalytic activity of ceria can be related to active oxygen formation provoked by the defective structure of ceria due to the presence of La³⁺ and Y³⁺. The benefit of Bi³⁺ doping on catalytic activity can be related to the reduction at low temperature both with Bi₂O₃ and ceria.

Nano CeO₂-based oxides with meso-pores have been synthesized by a solvothermal method.

Nickel and cobalt transfigured natural clay: a green catalyst for low-temperature catalytic soot oxidation

Modified 'natural clay' with Ni and Co nanoparticles explored as efficient catalyst for low-temperature soot oxidation activity studies.

Methane Combustion Using Pd Deposited on CeOx-MnOx/La-Al2O3 Pellistors

Pd deposited on CeO_x-MnO_x/La-Al₂O₃ has been prepared as a sensitive material for methane (CH₄) detection. The effect of different amounts (1.25%, 2.5% and 5%) of Pd loading has been investigated. The as prepared materials were deposited on Pt microcoils using a drop-coating method, as a way of developing pellistors operated using a Wheatstone bridge configuration. By spanning the operating temperature range between 300 °C and 550 °C, we established the linearity region as well as the maximum sensitivity towards 4900 ppm of CH₄. By making use of the sigmoid dependence of the output voltage signal from the Wheatstone bridge, the gas surface reaction and diffusion phenomena have been decoupled. The pellistor with 5% Pd deposited on CeO_x-MnO_x/La-Al₂O₃ exhibited the highest selective-sensitivity in the benefit of CH₄ detection against threshold limits of carbon monoxide (CO), sulfur dioxide (SO₂) and hydrogen sulfide (H₂S). Accordingly, adjusting the percent of Pd makes the preparation strategies of pellistors good candidates towards CH₄ detection.

Tuning the oxygen release properties of CeO2-based catalysts by metal–support interactions for improved gasoline soot combustion

CeO₂-supported Cu and Rh catalysts showed high soot combustion activities by their high oxygen release properties depending on moderate metal–oxygen bond energy.

Plasma-Assisted Selective Catalytic Reduction for Low-Temperature Removal of NOx and Soot Simulant

The challenge that needs to be overcome regarding the removal of nitrogen oxides (NOx) and soot from exhaust gases is the low activity of the selective catalytic reduction of NOx at temperatures fluctuating from 150 to 350 °C. The primary goal of this work was to enhance the conversion of NOx and soot simulant by employing a Ag/α-Al2O3 catalyst coupled with dielectric barrier discharge plasma. The results demonstrated that the use of a plasma-catalyst process at low operating temperatures increased the removal of both NOx and naphthalene (soot simulant). Moreover, the soot simulant functioned as a reducing agent for NOx removal, but with low NOx conversion. The high efficiency of NOx removal required the addition of hydrocarbon fuel. In summary, the combined use of the catalyst and plasma (specific input energy, SIE ≥ 60 J/L) solved the poor removal of NOx and soot at low operating temperatures or during temperature fluctuations in the range of 150–350 °C. Specifically, highly efficient naphthalene removal was achieved with low-temperature adsorption on the catalyst followed by the complete decomposition by the plasma-catalyst at 350 °C and SIE of 90 J/L.

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.