Benefiting from the exceptional selective catalytic reduction of NOx with ammonia (NH₃-SCR) activity, excellent N₂ selectivity, and superior hydrothermal durability, the Cu²⁺-exchanged zeolite catalyst with a chabazite structure (Cu-CHA) has been considered the predominant SCR catalyst in nitrogen oxide (NOx) abatement. However, sulfur poisoning remains one of the most significant deterrents to the catalyst in real applications. This review summarizes the NH₃-SCR reaction mechanism on Cu-CHA, including the active sites and the nature of hydrothermal aging resistance. On the basis of the NH₃-SCR reaction mechanism, the review gives a comprehensive summary of sulfate species, sulfate loading, emitted gaseous composition, and the impact of exposure temperature/time on Cu-CHA. The nature of the regeneration of sulfated catalysts is also covered in this review. The review gives a valuable summary of new insights into the matching between the design of NH₃-SCR activity and sulfur resistance, highlighting the opportunities and challenges presented by Cu-CHA. Guidance for future sulfur poisoning diagnosis, effective regeneration strategies, and a design for an efficient catalyst for the aftertreatment system (ATS) are proposed to minimize the deterioration of NOx abatement in the future. Finally, we call for more attention to be paid to the effects of PO₄^3- and metal co-cations with sulfur in the ATS.

Selective catalytic reduction filter (SDPF) technology constitutes a critical methodology for controlling nitrogen oxide (NOx) and particulate matter emissions from light-duty diesel vehicles. A series of SDPFs with different sulfur poisoning times and concentrations were prepared using the worldwide harmonized light vehicles test cycle (WLTC). Bench testing revealed that sulfur poisoning diminished the catalyst’s NH₃ storage capacity, impaired the transient NOx reduction efficiency, and induced premature ammonia leakage. After multiple sulfur poisoning incidents, the NOx reduction performance stabilized. Higher SO₂ concentrations accelerated catalyst deactivation and hastened the attainment of this equilibrium state. The characterization results for the catalyst indicate that the catalyst accumulated the same sulfur content after tail gas poisoning with different sulfur concentrations and that sulfur existed in the form of SO₄²⁻. The sulfur species in low-sulfur-poisoning-concentration catalysts mainly included sulfur ammonia and sulfur copper species, while high-sulfur-poisoning-concentration catalysts contained a higher proportion of sulfur copper species. Neither species type significantly altered the zeolite coating’s crystalline structure. Sulfur ammonia species could easily lead to a significant decrease in the specific surface area of the catalyst, which could be decomposed at 500 °C to achieve NOx reduction performance regeneration. In contrast, sulfur copper species required higher decomposition temperatures (600 °C), achieving only partial regeneration.

This study investigates the catalytic performance of platinum (Pt)-supported catalysts for nitric oxide (NO) oxidation in diesel vehicle exhaust aftertreatment systems, focusing on the effect of carrier modification. Pt catalysts were supported on γ-Al₂O₃, Ce-doped γ-Al₂O₃ (Ce-Al₂O₃), and La-doped γ-Al₂O₃ (La-Al₂O₃) via an excess impregnation method. Their physicochemical properties were characterized using inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), transmission electron microscopy (TEM), CO pulse chemisorption, and X-ray photoelectron spectroscopy (XPS). Catalytic activity for NO oxidation was evaluated under simulated diesel exhaust conditions, and the reaction mechanism was probed by in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) and NO temperature-programmed desorption (NO-TPD). The results show that La- and Ce-modified Pt catalysts (especially Pt/LaAl) exhibit superior aging resistance and NO oxidation activity compared to unmodified Pt/Al₂O₃. For fresh catalysts, Pt/LaAl-f achieves a Pt dispersion of 50.48% (vs. 24.72% for Pt/Al-f) and an average Pt particle size of 5.75 nm (vs. 6.64 nm for Pt/Al-f). After aging at 750 °C for 10 h, Pt/LaAl-a retains a specific surface area of 94.31 m² g⁻¹ (a 6.3% loss vs. 22.5% for Pt/Al-a) and a NO₂ proportion in NO_x of 42.1 ± 0.5% (vs. 28.3 ± 0.4% for Pt/Al-a). The enhanced performance of Pt/LaAl is attributed to the formation of Al₁₁La₃ intermetallic compounds, which provide additional NO adsorption sites and promote the generation of active intermediate species (e.g., bridging/chelating nitrates). In situ DRIFTS confirms abundant adsorbed nitrate/nitrite species on Pt/LaAl, while NO-TPD shows its NO adsorption capacity (89.6 µmol g⁻¹) is nearly twice that of Pt/Al (45.1 µmol g⁻¹). This work provides critical insights for designing high-efficiency NO_x purification catalysts for diesel exhaust and industrial waste gas treatment.

Passive NOx adsorber (PNA) is one of the important means to effectively reduce NOx emission control in the cold start of a diesel engine. A series of Pd/SSZ-13 catalysts with different SiO₂/Al₂O₃ ratios (11, 17, and 25) were prepared using the impregnation method. Furthermore, the effect of the SiO₂/Al₂O₃ ratio on the adsorption performance of Pd/SSZ-13 at low-temperature NOx under realistic exhaust conditions was studied. The results show that the Pd/SSZ-13 catalyst with a low SiO₂/Al₂O₃ ratio after loading Pd has a higher specific surface area and palladium ion content. There is a negative correlation between NOx adsorption performance and the SiO₂/Al₂O₃ ratio. After high-temperature heat treatment, the acid sites closely related to palladium species increase and palladium species will redisperse, producing more palladium ions. The palladium ions coexist in Pd/SSZ-13 in the form of Pd²⁺ and Pd⁺, among which Pd²⁺ is divided into two types: Z⁻Pd²⁺Z⁻ and Z⁻[Pd(II)OH]⁺. The NOx adsorption performance of the Pd/SSZ-13 catalyst was significantly improved, and the higher the SiO₂/Al₂O₃ ratio, the more obviously the advantage of NOx adsorption performance increased after heat treatment. The NOx adsorption kinetic model of the Pd/SSZ-13 catalyst under realistic exhaust conditions was most suitably described by the pseudo-first-order model.