Effect of Dopant Loading on the Structural and Catalytic Properties of Mn-Doped SrTiO3 Catalysts for Catalytic Soot Combustion

Fabrication of Mn-Doped SrTiO3/Carbon Fiber with Oxygen Vacancy for Enhanced Photocatalytic Hydrogen Evolution

With carbon fiber, it is difficult to load semiconductor photocatalysts and easy to shed off thanks to its smooth surface and few active groups, which has always been a problem in the synthesis of photocatalysts. In the study, SrTiO3 nanoparticles were loaded onto the Tencel fibers using the solvothermal method, and then the Tencel fibers were carbonized at a high temperature under the condition of inert gas to form carbon fibers, thus SrTiO3@CF photocatalytic composite materials with solid core shell structure were prepared. Meanwhile, Mn ions were added into the SrTiO3 precursor reagent in the solvothermal experiment to prepare Mn-doped Mn-SrTiO3@CF photocatalytic composite material. XPS and EPR tests showed that the prepared Mn-SrTiO3@CF photocatalytic composite was rich in oxygen vacancies. The existence of these oxygen vacancies formed oxygen defect states (VOs) below the conduction band, which constituted the capture center of photogenerated electrons and significantly improved the photocatalytic activity. The photocatalytic hydrogen experimental results showed that the photocatalytic hydrogen production capacity of Mn-SrTiO3@CF composite material with 5% Mn-doped was six times that of the SrTiO3@CF material, and the doping of Mn ions not only promoted the red shift of the light absorption boundary and the extension to visible light, but also improved the separation and migration efficiency of photocarriers. In the paper, the preparation method solves the difficulty of loading photocatalysts on CF and provides a new design method for the recycling of catalysts, and we improve the hydrogen production performance of photocatalysts by Mn-doped modification and the introduction of oxygen vacancies, which provides a theoretical method for the practical application of hydrogen energy.

Catalytic Mechanism of Oxygen Vacancies in Perovskite Oxides for Lithium-Sulfur Batteries

Defective materials have been demonstrated to possess adsorptive and catalytic properties in lithium-sulfur (Li-S) batteries, which can effectively solve the problems of lithium polysulfides (LiPSs) shuttle and sluggish conversion kinetics during charging and discharging of Li-S batteries. However, there is still a lack of research on the quantitative relationship between the defect concentration and the adsorptive-catalytic performance of the electrode. In this work, perovskites Sr_0.9 Ti_{1- x} Mn_x O_{3- δ} (STMn_x ) (x = 0.1-0.3) with different oxygen-vacancy concentrations are quantitatively regulated as research models. Through a series of tests of the adsorptive property and electrochemical performance, a quantitative relationship between oxygen-vacancy concentration and adsorptive-catalytic properties is established. Furthermore, the catalytic mechanism of oxygen vacancies in Li-S batteries is investigated using density functional theory calculations and in situ experiments. The increased oxygen vacancies can effectively increase the binding energy between perovskite and LiPSs, reduce the energy barrier of LiPSs decomposition reaction, and promote LiPSs conversion reaction kinetics. Therefore, the perovskite STMn_0.3  with high oxygen-vacancy concentrations exhibits excellent LiPSs adsorptive and catalytic properties, realizing high-efficiency Li-S batteries. This work is helpful to realize the application of the quantitative regulation strategy of defect engineering in Li-S batteries.

Evaluation of the catalytic oxidation of soot by CeOX-LaMnO3 at different O2 pressures synthesized by ultrasonic-assisted hydrothermal method

In this work, the synthesis of catalyst with perovskite structure and chemical formula La_1-XCe_XMnO₃ at x = 0 - 0.5 were successfully obtained by an ultrasonic-assisted hydrothermal method. Results show that the addition of Ce in La_1-XCe_XMnO₃ have not substantial effect in textural and morphological properties; however, the formation of a new crystalline phase with final composition CeO_X-La_1-XCe_XMnO₃ was detected at values x > 0.3. All synthesized catalysts were tested in the soot oxidation under both, loose and tight contact in 20% O₂/N₂ or 5% O₂/N₂ atmospheres. CeO_X-La_1-XCe_XMnO₃ at x = 0.3 resulted in the best catalytic activity with activation energy values of 57.9 kJ^.mol^-1. The interaction between Ce³⁺ and Mn⁴⁺ species in this catalyst can transfer electrons generating Mn³⁺ and Ce⁴⁺. This reduction from Mn⁴⁺ to Mn³⁺ is accompanied by migration of vacancies to the surface promoting the adsorbed oxygen from the gas phase, need for balancing the chemical states. By increasing the temperature above 300 °C, the bulk oxygen migration to the surface is enhanced being the responsible for the oxygen availability. The formation of CeO_X-La_1-XCe_XMnO₃ promotes a stable redox cycle allowing the reusability of this catalyst even at low oxygen pressures after three different reaction cycles.

Eliminación de carbonilla en gases de escape con catalizadores DeNOx. Determinación de parámetros cinéticos

Los catalizadores DeNOx se emplean en la eliminación de los óxidos de nitrógeno en vehículos diésel y, también, puede que entren en contacto con carbonilla o incluso sean utilizados como sistemas de reducción de NOx y soot simultáneamente (DPNR-Diesel Particulate NOx Reduction). Por ello, es importante profundizar en el mecanismo de interacción entre el Soot y el catalizador. Se ha utilizado un Soot Printex U modelo y un catalizador Pt-K/Al2O3, con el potasio en forma de óxido e hidroxicarbonato hidratado. Se ha estudiado mediante TG-MS el proceso de eliminación en diferentes atmósferas oxidantes. Los procesos han sido desacoplados mediante el establecimiento de la función de distribución de energía de activación. En ausencia de catalizador, se produce la combustión del carbonilla con el oxígeno molecular en fase gas a temperaturas alrededor de los 1100 K. En presencia de NO, la reducción tiene lugar a menor temperatura debido a su carácter más oxidante y a las especies de óxidos de nitrógeno retenidas y en fase gas. Si la carbonilla se encuentra en contacto con el catalizador Pt-K/Al2O3, los centros Pt-OH-K son los responsables de la eliminación vía gasificación a 780 K con una energía de activación alrededor de 85 kJ mol-1

Effect of A-site substitution on the simultaneous catalytic removal of NOx and soot by LaMnO3 perovskites

The simultaneous catalytic removal of NO_x and soot by La_1−xM_xMnO₃ (M = K, Sr, Pr; x = 0, 0.1, 0.2, 0.3) perovskites was investigated.

Facile synthesis of three-dimensional ordered macroporous Sr1−xKxTiO3 perovskites with enhanced catalytic activity for soot combustion

The appropriate incorporation of potassium into 3DOM SrTiO₃ perovskites effectively improved the catalytic performance for soot combustion.