Catalytic oxidation of diesel soot particulates over Pt substituted LaMn1-xPtxO3 perovskite oxides

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.

Role of La-based perovskite catalysts in environmental pollution remediation

Since the advent of the industrial revolution, there has been a constant need of efficient catalysts for abatement of industrial toxic pollutants. This phenomenon necessitated the development of eco-friendly, stable, and economically feasible catalytic materials like lanthanum-based perovskite-type oxides (PTOs) having well-defined crystal structure, excellent thermal, and structural stability, exceptional ionic conductivity, redox behavior, and high tunability. In this review, applicability of La-based PTOs in remediation of pollutants, including CO, NO x and VOCs was addressed. A framework for rationalizing reaction mechanism, substitution effect, preparation methods, support, and catalyst shape has been discussed. Furthermore, reactant conversion efficiencies of best PTOs have been compared with noble-metal catalysts for each application. The catalytic properties of the perovskites including electronic and structural properties have been extensively presented. We highlight that a robust understanding of electronic structure of PTOs will help develop perovskite catalysts for other environmental applications involving oxidation or redox reactions.

Oxygen Vacancy-Mediated Selective H2S Oxidation over Co-Doped LaFexCo1−xO3 Perovskite

Compared to the Claus process, selective H2S catalytic oxidation to sulfur is a promising reaction, as it is not subject to thermodynamic limitations and could theoretically achieve ~100% H2S conversion to sulfur. In this study, we investigated the effects of Co and Fe co-doping in ABO3 perovskite on H2S selective catalytic oxidation. A series of LaFexCo1−xO3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) perovskites were synthesized by the sol-gel method. Compared to LaFeO3 and LaCoO3, co-doped LaFexCo1−xO3 significantly improved the H2S conversion and sulfur selectivity at a lower reaction temperature. Nearly 100% sulfur yield was achieved on LaFe0.4Co0.6O3 under 220 °C with exceptional catalyst stability (above 95% sulfur yield after 77 h). The catalysts were characterized by XRD, BET, FTIR, XPS, and H2-TPR. The characterization results showed that the structure of LaFexCo1−xO3 changed from the rhombic phase of LaCoO3 to the cubic phase of LaFeO3 with Fe substitution. Doping with appropriate iron (x = 0.4) facilitates the reduction of Co ions in the catalyst, thereby promoting the H2S selective oxidation. This study demonstrates a promising approach for low-temperature H2S combustion with ~100% sulfur yield.

Experimental Evaluation on the Catalytic Activity of a Novel CeZrK/rGO Nanocomposite for Soot Oxidation in Catalyzed Diesel Particulate Filter

A nanostructured solid solution catalyst CeZrK/rGO for soot oxidation in catalyzed diesel particulate filter was synthesized using the dipping method. The reduced graphene oxide (rGO) was used as the catalyst carrier, and CeO2, ZrO2, and K2O were mixed with the molar ratio of 5:1:1, 5:2:2 and 5:3:3, which were referred to as Ce5Zr1K1/rGO, Ce5Zr2K2/rGO, and Ce5Zr3K3/rGO, respectively. The structure, morphology and catalytic activity of the CeZrK/rGO nanocomposites were thoroughly investigated and the results show that the CeZrK/rGO nanocomposites have nanoscale pore structure (36.1–36.9 nm), high-dispersion quality, large specific surface area (117.2–152.4 m2/g), small crystallite size (6.7–8.3 nm), abundant oxygen vacancies and superior redox capacity. The 50% soot conversion temperatures of Ce5Zr1K1/rGO, Ce5Zr2K2/rGO, and Ce5Zr3K3/rGO under tight contact condition were decreased to 352 °C, 339 °C and 358 °C respectively. The high catalytic activity of CeZrK/rGO nanocomposites can be ascribed to the following factors: the doping of Zr and K ions causes the nanocrystalline phase formation in CeZrK solid solutions, reduces the crystallite size, generates abundant oxygen vacancies and improves redox capacity; the rGO as a carrier provides a large specific surface area, thereby improving the contact between soot and catalyst.

Synergistic Effects of Multicomponents Produce Outstanding Soot Oxidation Activity in a Cs/Co/MnOx Catalyst

The control of soot emission from diesel vehicles is of extraordinary importance to the environment, and catalytic removal of soot is a highly effective and clean method. Here, we report a novel, non-noble metal catalyst for application in the catalytic combustion of soot with superb activity and resistance to H₂O and SO₂. MnO_x oxide was prepared via a hydrothermal method, and then, Cs and Co were loaded on MnO_x by impregnation. The 5%Cs/1%Co/MnO_x catalyst displayed excellent catalytic activity with values of T₁₀ (332 °C), T₅₀ (371 °C), and T₉₀ (415 °C) under loose contact. The as-prepared catalysts were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), H₂ temperature-programmed reduction (TPR), O₂ temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS). The results suggest that, after the introduction of Cs and Co into the MnO_x oxide, more NO₂ molecules take part in soot oxidation, exhibiting higher NO₂ utilization efficiency; this is due to the synergistic effects of multiple components (Cs, Co, and Mn) promoting the generation of more surface-active oxygen and then accelerating the reaction between NO₂ and soot. This study provides significant insights into the development of high-efficiency catalysts for soot oxidation, and the developed 5%Cs/1%Co/MnO_x catalyst is a promising candidate for application in diesel particulate filters.

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.

Gaseous and Particulate Emissions from a Chimneyless Biomass Cookstove Equipped with a Potassium Catalyst

Approximately three billion people cook with solid fuels, mostly wood, on open fires or rudimentary stoves. These traditional cooking methods produce particulate matter and carbon monoxide known to cause significant respiratory health problems, especially among women and children, who often have the highest exposure. In this work, an inexpensive potassium-based catalyst was incorporated in a chimneyless biomass cookstove to reduce harmful emissions through catalytic oxidation. Potassium titanate was identified as an effective and stable oxidation catalyst capable of oxidizing particulate matter and carbon monoxide. Using a cordierite monolith to incorporate potassium titanate within a bespoke, rocket-style, improved cookstove led to a 36% reduction in particulate matter emissions relative to a baseline stove with a blank monolith and a 26% reduction relative to a stove with no monolith. Additionally, the catalytic stove reduced particulate matter emissions by 82%, reduced carbon monoxide emissions by 70%, and improved efficiency by 100% compared to a carefully tended, three-stone fire. Potassium titanate was also shown to oxidize carbon monoxide at temperatures as low as 500 °C, or as low as 300 °C when doped with copper or cobalt.