Platinum-supported catalysts on modified γ-Al2O3 carriers for enhanced NO oxidation in diesel exhaust aftertreatment

Abstract

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.