Promoting Effects of Barium Substitution on the Catalytic Performances of FeCeO2−δ for Soot Oxidation

Alkali/alkaline-earth metal-modified MnOx supported on three-dimensionally ordered macroporous-mesoporous TixSi1-xO2 catalysts: Preparation and catalytic performance for soot combustion

The performance of catalysts used in after-treatment systems is the key factor for the removal of diesel soot, which is an important component of atmospheric fine particle emissions. Herein, three-dimensionally ordered macroporous-mesoporous Ti_xSi_1-xO₂ (3DOM-m Ti_xSi_1-xO₂) and its supported MnO_x catalysts doped with different alkali/alkaline-earth metals (AMnO_x/3DOM-m Ti_0.7Si_0.3O₂ (A: Li, Na, K, Ru, Cs, Mg, Ca, Sr, Ba)) were prepared by mesoporous template (P123)-assisted colloidal crystal template (CCT) and incipient wetness impregnation methods, respectively. Physicochemical characterizations of the catalysts were performed using scanning electron microscopy, X-ray diffraction, N₂ adsorption-desorption, H₂ temperature-programmed reduction, O₂ temperature-programmed desorption, NO temperature-programmed oxidation, and Raman spectroscopy techniques; then, we evaluated their catalytic performances for the removal of diesel soot particles. The results show that the 3DOM-m Ti_0.7Si_0.3O₂ supports exhibited a well-defined 3DOM-m nanostructure, and AMnO_x nanoparticles with 10-50 nm were evenly dispersed on the inner walls of the uniform macropores. In addition, the as-prepared catalysts exhibited good catalytic performance for soot combustion. Among the prepared catalysts, CsMnO_x/3DOM-m Ti_0.7Si_0.3O₂ had the highest catalytic activity for soot combustion, with T₁₀, T₅₀, and T₉₀ (the temperatures corresponding to soot conversion rates of 10%, 50%, and 90%) values of 285, 355, and 393°C, respectively. The high catalytic activity of the CsMnO_x/3DOM-m Ti_0.7Si_0.3O₂ catalysts was attributed to their excellent low-temperature reducibility and homogeneous macroporous-mesoporous structure, as well as to the synergistic effects between Cs and Mn species and between CsMnO_x and the Ti_0.7Si_0.3O₂ support.

Property and Reactivity Relationships of Co3O4 with Diverse Nanostructures for Soot Oxidation

Cobalt oxide (Co₃O₄) nanostructures with different morphologies (nanocubes, nanoplates, and nanoflowers) were synthesized by a simple hydrothermal method and used for catalytic oxidation of soot particles. Through the study of the physicochemical properties of the catalysts, the key factors affecting the performance of soot oxidation were investigated. The results showed that all three kinds of Co₃O₄ nanocrystals exhibited excellent low-temperature activity in catalytic oxidation of soot, and the Co₃O₄ nanoflowers showed higher oxidation activity of soot compared with Co₃O₄ nanocubes and Co₃O₄ nanoplates, whose T _m was only 370 °C. The excellent activity of Co₃O₄ nanoflowers was due to the large amount of Co³⁺ and lattice oxygen on their surface and highly defective structure, which promoted the adsorption and activation of oxygen species. The large crystallite size and few surface defects were the main reasons for the poor catalytic performance of Co₃O₄ nanocubes. During soot oxidation, the crystallite size of the catalysts and the contact between the catalysts and soot played a significant role in the catalytic performance.

Soot Oxidation over γ-Al2O3-Supported Manganese-Based Binary Catalyst in a Dielectric Barrier Discharge Reactor

In this work, soot oxidation was conducted over a series of Mn-X/γ-Al2O3 (M = Ce, Co and Cu) binary catalysts in a dielectric barrier discharge reactor. The soot conversion in the plasma–catalytic system was in the order of Mn/γ-Al2O3 (57.7%) > Mn-Co/γ-Al2O3 (53.9%) > Mn-Ce/γ-Al2O3 (51.6%) > Mn-Cu/γ-Al2O3 (47.7%) during the 30 min soot oxidation process at 14 W and 150 °C. Meanwhile, the doping of Ce, Co and Cu slightly improved the CO2 selectivity of the process by 4.7% to 10.3% compared to soot oxidation over Mn/γ-Al2O3.It is worth to note that the order of CO2 selectivity was in the opposite order with soot oxidation rate. The effects of discharge power, oxygen content in the carrier gas and reaction temperature on plasma–catalytic soot oxidation was systematically analyzed. The catalyst characterizations, including N2 adsorption–desorption, X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction by H2 and temperature-programmed desorption of O2, were conducted to illustrate the reaction mechanisms of plasma–catalytic soot oxidation and reaction pathways.