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.

Insight into phase structure-dependent soot oxidation activity of K/MnO2 catalyst

In the present study, two nanosized MnO₂ with β and δ phase structures and potassium loaded MnO₂ catalysts with varied K loading amounts (denoted as K/MnO₂) were prepared. Temperature programmed oxidation and isothermal reactions in loose contact modes were employed to examine the soot oxidation activity of the as-prepared catalysts. Characterization results show that as compared with β-MnO₂, δ-MnO₂ has larger surface area and higher content of hydroxyl groups. Upon K loading, abundant hydroxyl groups in δ-MnO₂ effectively sequestrate K cation to form bound K species and free K species are available only at K loading above 3.0 wt.%. In contrast, the majority of K species present as free state in β-MnO₂ even at a K loading of 1.0 wt.% due to its very low hydroxyl group content. The O₂ temperature-programmed desorption (O₂-TPD) demonstrates that the catalysts with free K species exhibit strong ability in activating gaseous O₂, whereas the catalysts only having bound K display minor O₂ activation capability. As a result, despite of slightly lower activity of β-MnO₂ than δ-MnO₂, the K/β-MnO₂ catalysts exhibit substantially higher activities than K/δ-MnO₂ catalysts with identical K loadings. The finding in this study clearly demonstrates that for MnO₂ based catalysts, the enhancement of catalytic activity for soot oxidation is highly K loading amount dependent and the dependency is strongly associated with the phase structure of MnO₂.

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.

Enhanced activity and sulfur resistance of Cu- and Fe-modified activated carbon for the reduction of NO by CO from regeneration gas

The reduction of NO by CO was proposed to be applied for regeneration gas to remove NOx from industrial flue gas with activated carbon purification technology.

Application Prospect of K Used for Catalytic Removal of NOx, COx, and VOCs from Industrial Flue Gas: A Review

NOx, COx, and volatile organic compounds (VOCs) widely exist in motor vehicle exhaust, coke oven flue gas, sintering flue gas, and pelletizing flue gas. Potassium species have an excellent promotion effect on various catalytic reactions for the treatment of these pollutants. This work reviews the promotion effects of potassium species on the reaction processes, including adsorption, desorption, the pathway and selectivity of reaction, recovery of active center, and effects on the properties of catalysts, including basicity, electron donor characteristics, redox property, active center, stability, and strong metal-to support interaction. The suggestions about how to improve the promotion effects of potassium species in various catalytic reactions are put forward, which involve controlling carriers, content, preparation methods and reaction conditions. The promotion effects of different alkali metals are also compared. The article number about commonly used active metals and promotion ways are also analyzed by bibliometric on NOx, COx, and VOCs. The promotion mechanism of potassium species on various reactions is similar; therefore, the application prospect of potassium species for the coupling control of multi-pollutants in industrial flue gas at low-temperature is described.

In-situ modified the surface of Pt-doped perovskite catalyst for soot oxidation

In-situ modification is studied in this work on LaCo_1-xPt_xO₃ for soot oxidation. A series of perovskite catalysts LaCo_1-xPt_xO₃ (by sol-gel method) are modified with 30% H₂O₂. XRD, TEM, SEM, BET, XPS, Raman, in-situ DRIFTS, H₂-TPR and TGA are used to investigate physicochemical properties of catalysts. TGA results show that all doped catalysts have a lower temperature of soot conversion, especially LaCo_0.94Pt_0.06O₃ (T₅₀ = 437 °C). The T₅₀ of the catalyst with modification by H₂O₂ solution decreases at least 20 °C compared with the doped catalysts. A highly symmetrical structure and an obvious amorphous layer about 3-5 nm are observed in the modified catalysts. According to the XPS study, the symmetrical structure benefits to the movement of oxygen vacancy thus catalyst captures more adsorbed oxygen (about 95%). And the amorphous surface could adsorb more oxygen species. In addition, all catalysts show excellent aging resistance performance. The reaction mechanism of catalyst for soot oxidation is presented in the end.

Revealing the unexpected promotion effect of diverse potassium precursors on α-MnO2 for the catalytic destruction of toluene

The alkali metal potassium has the functions of structure promotion and electronic modulation in metal oxides.

Three-dimensionally ordered macroporous K0.5MnCeOx/SiO2 catalysts: facile preparation and worthwhile catalytic performances for soot combustion

A series of novel catalysts with three-dimensionally ordered macroporous structures and active-component nanoparticles, exhibiting excellent catalytic performance for soot combustion, were fabricated.

Construction of a hollow structure in La0.9K0.1CoO3−δ nanofibers via grain size control by Sr substitution with an enhanced catalytic performance for soot removal

The hollow structure is formed by Sr²⁺ doping in La_0.9K_0.1CoO_3−δ nanofibers for decreasing the grain size, which can improve the contact efficiency of soot–catalyst–gas as well as the intrinsic activity, responsible for the enhancement in activity.

The relationship between the chemical state of Pd species and the catalytic activity for methane combustion on Pd/CeO2

Three Pd/CeO₂ catalysts are synthesized by reduction-deposition and an impregnation method (IMP) to clarify how the chemical state of Pd influences the catalytic performance for CH₄ combustion.

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.

Bridging the gap between tight and loose contacts for soot oxidation by vanadium doping of cryptomelane nanorods catalyst using NO2 as an oxygen carrier

The effect of the V-doping of cryptomelane on bridging the tight-loose contact gap in NO-assisted catalytic soot oxidation was investigated.