Hierarchical Porous K-OMS-2/3DOM-m Ti0.7Si0.3O2 Catalysts for Soot Combustion: Easy Preparation, High Catalytic Activity, and Good Resistance to H2O and SO2

A review of regeneration mechanism and methods for reducing soot emissions from diesel particulate filter in diesel engine

With the global emphasis on environmental protection and the proposal of the climate goal of "carbon neutrality," countries around the world are calling for reductions in carbon dioxide, nitrogen oxide, and particulate matter pollution. These pollutants have severe impacts on human lives and should be effectively controlled. Engine exhaust is the most serious pollution source, and diesel engine is an important contributor to particulate matter. Diesel particulate filter (DPF) technology has proven to be an effective technology for soot control at the present and in the future. Firstly, the exacerbating effect of particulate matter on human infectious disease viruses is discussed. Then, the latest developments in the influence of key factors on DPF performance are reviewed at different observation scales (wall, channel, and entire filter). In addition, current soot catalytic oxidant schemes are presented in the review, and the significance of catalyst activity and soot oxidation kinetic models are highlighted. Finally, the areas that need further research are determined, which has important guiding significance for future research. Current catalytic technologies are focused on stable materials with high mobility of oxidizing substances and low cost. The challenge of DPF optimization design is to accurately calculate the balance between soot and ash load, DPF regeneration control strategy, and exhaust heat management strategy.

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.

Enhanced degradation and mineralization of estriol over ZrO2/OMS-2 nanocomposite: Kinetics, pathway and mechanism

Although remarkable progresses have been achieved in the exploration of new and efficient catalytic systems for efficient degradation of estriol, there are only very few available reports providing high mineralization of estriol. Hence, it is still a serious challenge to develop the novel and efficient methods for enhanced degradation and mineralization of estriol due to its serious threat to environment and human health. Herein, this study proposes a series of ZrO₂ modified manganese oxide octahedral molecular sieve (ZrO₂/OMS-2) nanocomposites as efficient catalysts for enhanced degradation and mineralization of estriol via PMS activation at 30 °C. Among them, ZrO₂/OMS-2-27% provided the highest degradation efficiency (95%) and mineralization degrees (70.1%), which exceeded most reported catalytic systems, in the catalytic degradation of estriol. These quenching tests and EPR analysis had confirmed that O₂•^- and ¹O₂ were primary reactive oxygen species (ROS) in the ZrO₂/OMS-2-27%/PMS system, contrary to the OMS-2/PMS system for which SO₄•^- and OH• are primary ROS. This might be due to the abundant O-containing surface functional groups of ZrO₂/OMS-2-27%. This work not only provides a facile and high-efficiency methodology for the construction of Mn-based nanomaterial, but also proposes a new and efficient nano-catalyst for estriol removal.

Revealing the promoting effect of multiple Mn valences on the catalytic activity of CeO2 nanorods toward soot oxidation

Mn-modified CeO₂ nanomaterials have attracted extensive attention as efficient and promising catalysts for soot combustion due to their low cost and high catalytic activity. However, a detailed mechanism of how Mn promotes soot oxidation over CeO₂ is still not clearly elucidated, which is crucial to further optimize the catalyst for achieving its practical applications. We here report a Mn-doped CeO₂ catalyst with tunable surface Mn chemical valence states to study the Mn-promoting mechanism for improving CeO₂ catalyst activity in soot oxidation. Experimental results show that Mn-doped CeO₂ nanorods with surface Mn chemical valence states being optimized (Mn_0.19Ce_0.81O₂) can lower the eliminating temperature of soot to 410 °C (T₉₀) when in a loose contact and exhibit a strong resistance towards water molecules. The catalytic performances of Mn_0.19Ce_0.81O₂ nanorods are comparable with those of other reported oxide catalysts both in the mimetic realistic and ideal reaction environments. Detailed characterization and theoretical calculation results demonstrate that balanced multiple Mn valences can dramatically enhance the catalysts' redox properties and their ability to activate O₂ molecules, as well as improve the dynamic contact efficiency during the oxidation, which synergistically result in superior catalytic performances. This work might provide insight for the future design and preparation of catalysts to efficiently eliminate soot particles.

Preparation of 3DOM ZrTiO4 Support, WxCeMnOδ/3DOM ZrTiO4 Catalysts, and Their Catalytic Performance for the Simultaneous Removal of Soot and NOx

As an efficient and durable engine, a diesel engine has a broad application. However, soot particles (PM) and nitrogen oxides (NO_x) coming from diesel engines are the main causes of air pollution, so it is necessary to design and prepare an effective catalyst for the simultaneous elimination of PM and NO_x. In this work, a novel 3DOM ZrTiO₄ support and a series of W_xCeMnO_δ/3DOM ZrTiO₄ catalysts (where x indicates the wt% of W) were designed and fabricated by the colloidal crystal template technique. Among the as-prepared catalysts, the W₁CeMnO_δ/3DOM ZrTiO₄ catalyst exhibits the highest NO conversion rate (52%) at the temperature of maximum CO₂ concentration (474°C) and achieves 90% NO conversion in the temperature range of 250–396°C. The excellent catalytic performance is associated with the macroporous structure, abundant oxygen vacancies, sufficient acid sites, and the synergistic effect among the active components. The possible reaction mechanisms of W_xCeMnO_δ/3DOM ZrTiO₄ catalysts were also discussed based on the characterization results.

Facile preparation, catalytic performance and reaction mechanism of MnxCo1-xOδ/3DOM-m Ti0.7Si0.2W0.1Oy catalysts for the simultaneous removal of soot and NOx

In this work, three-dimensionally ordered macroporous-mesoporous Ti0.7Si0.2W0.1Oy (3DOM-m TiSiWO) supported MnxCo1-xOδ catalysts with different x values were prepared using the colloidal crystal template method and incipient wetness impregnation method. The...

Facilitating Catalytic Purification of Auto-Exhaust Carbon Particles via the Fe2O3{113} Facet-dependent Effect in Pt/Fe2O3 Catalysts

The purification efficiency of auto-exhaust carbon particles in the catalytic aftertreatment system of vehicle exhaust is strongly dependent on the interface nanostructure between the noble metal component and oxide supports. Herein, we have elaborately synthesized the catalysts (Pt/Fe₂O₃-R) of Pt nanoparticles decorated on the hexagonal bipyramid α-Fe₂O₃ nanocrystals with co-exposed twelve {113} and six {104} facets. The area ratios (R) of co-exposed {113} to {104} facets in α-Fe₂O₃ nanocrystals were adjusted by the fluoride ion concentration in the hydrothermal method. The strong Pt-Fe₂O₃{113} facet interaction boosts the formation of coordination unsaturated ferric sites for enhancing adsorption/activation of O₂ and NO. Pt/Fe₂O₃-R catalysts exhibited the Fe₂O₃{113} facet-dependent performance during catalytic purification of soot particles in the presence of H₂O. Among the catalysts, the Pt/Fe₂O₃-19 catalyst exhibits the highest catalytic activities (T₅₀ = 365 °C, TOF = 0.13 h^-1), the lowest apparent activation energy (69 kJ mol^-1), and excellent catalytic stability during soot purification. Combined with the results of characterizations and density functional theory calculations, the catalytic mechanism is proposed: the active sites located at the Pt-Fe₂O₃{113} interface can boost the key step of NO oxidation to NO₂. The crystal facet engineering is an effective strategy to obtain efficient catalysts for soot purification in practical applications.

Preparation of K Modified Three-Dimensionally Ordered Macroporous MnCeOx/Ti0.7Si0.3O2 Catalysts and Their Catalytic Performance for Soot Combustion

Soot particles in diesel engine exhaust is one of the main reasons for hazy weather and elimination of them is urgent for environmental protection. At present, it is still a challenge to develop new catalysts with high efficiency and low cost. In this paper, a kind of K modified three-dimensionally ordered macroporous (3DOM) MnCeOx/Ti0.7Si0.3O2 catalysts are designed and synthesized by a sample method. Due to the macroporous structure and synergistic effect of K, Mn, and Ce, the KnMnCeOx/Ti0.7Si0.3O2 (KnMnCeOx/M-TSO) catalysts exhibit good catalytic performance for soot combustion. The catalytic activity of K0.5MnCeOx/M-TSO was the best, and the T10, T50, and T90 are 287, 336, and 367 °C, respectively. After the prepared catalyst was doped with K, the physicochemical properties and catalytic performance changed significantly. In addition, the K0.5MnCeOx/M-TSO catalyst also somewhat exhibits sulfur tolerance owing to it containing Ti. Because of its simple synthesis, high activity, and low cost, the prepared KnMnCeOx/M-TSO catalysts are regarded as a promising candidate for application.