Au Nanoparticle/MgAl2O4 Catalysts via Acid Etching for Formaldehyde Oxidation

Spinel is a type of oxide and is rich in defect sites, which can play a vital role in anchoring noble metals. In this work, we subjected the MgAl2O4 spinel to nitric acid etching to generate more surface defects. Subsequently, low-loading (0.3–0.4 wt %) Au nanoparticle/MgAl2O4 catalysts were obtained by the precipitation method. Analysis of characterization results showed that the nitric acid treatment effectively removed Mg ions, simultaneously creating defects and enhancing the dispersion of Au nanoparticles. Compared to Au/MgAl2O4, Au/MgAl2O4–O (carrier pretreated by nitric acid) exhibited superior formaldehyde (HCHO) oxidation performance, achieving complete HCHO oxidation at 40 °C, due to the enhanced ability to activate H2O. In situ Diffuse Reflectance Infrared Fourier Transform (in situ DRIFT) study revealed that both the Au/MgAl2O4 and Au/MgAl2O4–O catalysts follow the same reaction mechanism: HCHO → DOM (dioxymethylene) → formate → CO2 + H2O, with formate oxidation as the rate-determining step. This study explored the effect of the pretreatment of spinel-supported precious metal catalysts on HCHO oxidation at low temperatures, providing more opportunities for the synthesis of multidefect nanoscale catalysts.