A Review on the Impact of SO2 on the Oxidation of NO, Hydrocarbons, and CO in Diesel Emission Control Catalysis

Highly Reactive Peroxide Species Promoted Soot Oxidation over an Ordered Macroporous Ce0.8Zr0.2O2 Integrated Catalyzed Diesel Particulate Filter

Particulate matter, represented by soot particles, poses a significant global environmental threat, necessitating efficient control technology. Here, we innovatively designed and elaborately fabricated ordered hierarchical macroporous catalysts of Ce0.8Zr0.2O2 (OM CZO) integrated on a catalyzed diesel particulate filter (CDPF) using the self-assembly method. An oxygen-vacancy-enriched ordered macroporous Ce0.8Zr0.2O2 catalyst (VO-OM CZO) integrated CDPF was synthesized by subsequent NaBH4 reduction. The VO-OM CZO integrated CDPF exhibited a markedly enhanced soot oxidation activity compared to OM CZO and powder CZO coated CDPFs (T50: 430 vs 490 and 545 °C, respectively). The well-defined OM structure of the VO-OM CZO catalysts effectively improves the contact efficiency between soot and the catalysts. Meanwhile, oxygen vacancies trigger the formation of a large amount of highly reactive peroxide species (O22-) from molecular oxygen (O2) through electron abstraction from the three adjacent Ce3+ (3Ce3+ + Vö + O2 → 3Ce4+ + O22-), contributing to the efficient soot oxidation. This work demonstrates the fabrication of the ordered macroporous CZO integrated CDPF and reveals the importance of structure and surface engineering in soot oxidation, which sheds light on the design of highly efficient PM capture and removal devices.

Strong metal support interaction (SMSI) and MoO3 synergistic effect of Pt-based catalysts on the promotion of CO activity and sulfur resistance

In industrial applications, Pt-based catalysts for CO oxidation have the dual challenges of CO self-poisoning and SO2 toxicity. This study used synthetic Keggin-type H3PMo12O40 (PMA) as the site of Pt, and the Pt-MoO3 produced by decomposition of PMA was anchored to TiO2 to construct the dual-interface structure of Pt-MoO3 and Pt-TiO2, abbreviated as Pt-P&M/TiO2. Pt-0.125P&M/TiO2 with a molar ratio of Pt to PMA of 8:1 showed both good CO oxidation activity and SO2 tolerance. In the CO activity test, the CO complete conversion temperature T100 of Pt-0.125P&M/TiO2 was 113 ℃ (compared with 135 ℃ for Pt/TiO2). In the SO2 resistance test, the conversion efficiency of Pt-0.125P&M/TiO2 at 170 ℃ remained at 60% after 72 h, while that of Pt/TiO2 was only 13%. H2-TPR and XPS tests revealed that lattice oxygen provided by TiO2 and hydroxyl produced by MoO3 increased the CO reaction rate on Pt. According to the DFT theoretical calculation, the electronegative MoO3 attracted the d-orbital electrons of Pt, which reduced the adsorption energy of CO and SO2 from - 4.15 eV and - 2.54 eV to - 3.56 eV and - 1.52 eV, respectively, and further weakened the influence of strong CO adsorption and SO2 poisoning on the catalyst. This work explored the relationship between catalyst structure and catalyst performance and provided a feasible technical idea for the design of high-performance CO catalysts in industrial applications.

Efficient destruction of basic organo-nitrogenous compounds in liquid hydrocarbon fuel using ascorbic acid/H2O2 system under ambient condition

Due to the limitations of the conventional refinery methods, development of a new method such as oxidative denitrogenation (ODN) is highly desirable. This study described a novel ODN to remove organo-nitrogenous compounds (ONCs) in liquid fuel by ascorbic acid (AscH2) and H2O2 redox system under ambient conditions. Seven ONCs including pyridine, quinoline, acridine, 7,8-benzoquinoline, indole, N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF) were chosen to assess the fuel-denitrified ability of the AscH2/H2O2 system. The results showed that the basic group of ONCs (pyridine, quinoline, and acridine) can be effectively removed (removal ratio > 95 %) while the removal efficiency of water-soluble compounds (7,8-benzoquinoline, NMP, and DMF) was moderate (61-68 %) under a mild temperature (30 °C) and atmospheric pressure. Free radical quenching and electron paramagnetic resonance experiments confirmed that hydroxyl and AscH2 radicals played a major role in the degradation of ONCs. The degraded products of quinoline were analyzed by gas chromatography-mass spectroscopy and ion chromatography. Based on the identified intermediate products, a putative reaction pathway majorly involving three steps of N-onium formation, transfer hydrogenation, and free radical oxidative ring-opening was suggested for the quinoline degradation. The presented approach can be performed at a normal temperature and pressure and will live up to expectations in the pre-denitrogenation and selective removal of basic ONCs in fuel oils.

Designing main-group catalysts for low-temperature methane combustion by ozone

The catalytic combustion of methane at a low temperature is becoming increasingly key to controlling unburned CH₄ emissions from natural gas vehicles and power plants, although the low activity of benchmark platinum-group-metal catalysts hinders its broad application. Based on automated reaction route mapping, we explore main-group elements catalysts containing Si and Al for low-temperature CH₄ combustion with ozone. Computational screening of the active site predicts that strong Brønsted acid sites are promising for methane combustion. We experimentally demonstrate that catalysts containing strong Bronsted acid sites exhibit improved CH₄ conversion at 250 °C, correlating with the theoretical predictions. The main-group catalyst (proton-type beta zeolite) delivered a reaction rate that is 442 times higher than that of a benchmark catalyst (5 wt% Pd-loaded Al₂O₃) at 190 °C and exhibits higher tolerance to steam and SO₂. Our strategy demonstrates the rational design of earth-abundant catalysts based on automated reaction route mapping.

Advances in emission control of diesel vehicles in China

Diesel vehicles have caused serious environmental problems in China. Hence, the Chinese government has launched serious actions against air pollution and imposed more stringent regulations on diesel vehicle emissions in the latest China VI standard. To fulfill this stringent legislation, two major technical routes, including the exhaust gas recirculation (EGR) and high-efficiency selective catalytic reduction (SCR) routes, have been developed for diesel engines. Moreover, complicated aftertreatment technologies have also been developed, including use of a diesel oxidation catalyst (DOC) for controlling carbon monoxide (CO) and hydrocarbon (HC) emissions, diesel particulate filter (DPF) for particle mass (PM) emission control, SCR for the control of NOx emission, and an ammonia slip catalyst (ASC) for the control of unreacted NH₃. Due to the stringent requirements of the China VI standard, the aftertreatment system needs to be more deeply integrated with the engine system. In the future, aftertreatment technologies will need further upgrades to fulfill the requirements of the near-zero emission target for diesel vehicles.

Insight into the Effect of Oxygen Vacancy Prepared by Different Methods on CuO/Anatase Catalyst for CO Catalytic Oxidation

In this study, CuO loaded on anatase TiO2 catalysts (CuO/anatase) with oxygen vacancies was synthesized via reduction treatments by NaHB4 and H2 (CuO/anatase-B, CuO/anatase-H), respectively. The characterizations suggest that different reduction treatments bring different concentration of oxygen vacancies in the CuO/anatase catalysts, which finally affect the CO catalytic performance. The CuO/anatase-B and CuO/anatase-H exhibit CO conversion of 90% at 182 and 198 °C, respectively, which is lower than what occurred for CuO/anatase (300 °C). The XRD, Raman, and EPR results show that the amount of the oxygen vacancies of the CuO/anatase-H is the largest, indicating a stronger reduction effect of H2 than NaHB4 on the anatase surface. The in situ DRIFTS results exhibit that the Cu sites are the adsorption sites of CO, and the oxygen vacancies on the anatase can active the O2 molecules into reactive oxygen species. According to the in situ DRIFTS results, it can be concluded that in the CO oxidation reaction, only the CuO/anatase-H catalyst can be carried out by the Mvk mechanism, which greatly improves its catalytic efficiency. This study explained the reaction mechanisms of CO oxidation on various anatase surfaces, which offers detailed insights into how to prepare suitable catalysts for low-temperature oxidation reactions.