Solvothermal Synthesis of MgO/ZrO2 and Its Enhanced Mechanism for Catalytic Oxidation of NO

Magnesium oxide-modified zirconia (MgO/ZrO2) catalysts were synthesized using conventional sol-gel (SG) and a combined sol-gel-solvothermal (SG-ST) method to systematically investigate the effect of solvothermal treatment on the catalyst’s microstructure and its performance in nitric oxide (NO) oxidation. The catalysts were characterized by X-ray diffraction, scanning electron microscopy, N2 physisorption, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction (H2-TPR), and O2 temperature-programmed desorption (O2-TPD). Evaluation of catalytic activity demonstrated that the SG-ST catalyst was superior, achieving 75.8% NO conversion at 300°C and exhibiting a significantly broader operating temperature window compared to the SG catalyst. Characterization results indicated that the solvothermal process effectively inhibited particle agglomeration, yielding a more regular morphology, a substantially larger specific surface area (34.28 m2·g−1 versus 6.21 m2·g−1), and a higher pore volume (0.225 cm3·g−1 versus 0.031 cm3·g−1). Further, this method promoted the formation of additional surface oxygen vacancies and active oxygen species (the Oβ+Oγ ratio increased to 34.83% from 30.39%) and optimized the surface acid-base properties by generating more Lewis basic sites. These synergistic modifications enhanced the catalyst’s redox properties and improved its capacity for NO adsorption and activation. This study clarifies the mechanism by which the solvothermal method enhances the performance of MgO/ZrO2 catalysts, providing a practical strategy for designing efficient denitrification catalysts.