A Mass Transfer Study on Formaldehyde Oxidation Using Anodic Aluminum Oxide-Based Structured Catalysts

Thermocatalytic oxidation represents the most effective and eco-friendly approach for formaldehyde abatement. This study employed anodic aluminum oxide (AAO) as support and developed a plate-structured K–Ag/La–CeO2/AAO catalyst. The AAO support was hydrated to form high-surface-area γ-Al2O3, followed by a sequence of oxygen-vacancy-enriched surface modifications and Ag catalytic phase loading. The 3-layer AAO catalyst assembly achieved ∼40% formaldehyde conversion at 30 °C and a short residence time of 0.13 s, compared to only 2.3% for a conventional 3 mm extrudate catalyst. The plate-structured catalyst exhibited a turnover frequency (TOF) 1.1 times higher than the extrudate catalyst at 90 °C and 10 times higher at 60 °C. Under the intraparticle diffusion-limit regime, the AAO catalyst delivered a reaction rate constant of 30.7 s–1 at 90 °C, 1.4 times higher than the extrudate catalyst. Due to the small characteristic size (40 μm), the AAO catalyst retained an effectiveness factor of 1 across a wide range of effective diffusivity. COMSOL simulations confirmed enhanced mass transfer of this structure catalyst, with a 5-layer configuration achieving 92% conversion at a high face velocity of 2.0 m/s. With superior intrinsic activity and enhanced mass transfer characteristics, AAO structured catalysts provide a promising pathway for process intensification in low-temperature air purification applications.