Highly efficient Ru/CeO2 catalysts for formaldehyde oxidation at low temperature and the mechanistic study

Abstract

Formaldehyde (HCHO) elimination at low temperature is of great interest for indoor air purification. In this work, 1 wt% Ru supported on CeO₂ and Al₂O₃ catalysts were prepared by an impregnation method and subsequently tested for the catalytic oxidation of HCHO at low temperature. The activity of the Ru/CeO₂ catalyst was significantly superior to the Ru/Al₂O₃ catalyst, achieving complete conversion of 130 ppm HCHO at 90 °C with a GHSV of 100 000 mL g_cat⁻¹ h⁻¹. Brunauer–Emmett–Teller (BET) measurements, X-ray powder diffraction (XRD), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray photoelectron spectroscopy (XPS) and H₂-temperature-programmed reduction (H₂-TPR) were carried out to characterize the physical and chemical properties of the catalysts. The results revealed that RuO_x species, rather than Ru⁰, were directly responsible for the HCHO oxidation over Ru/CeO₂, and the excellent performance of Ru/CeO₂ was mainly attributed to the strong interaction between Ru and CeO₂, which induced a high dispersion and high redox capacity of RuO_x species. The reaction mechanism of HCHO oxidation was also investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). It was shown that the HCHO oxidation over the Ru/CeO₂ and Ru/Al₂O₃ catalysts followed the same pathway of the direct formate oxidation (HCHO → HCOO + OH → H₂O + CO₂).