Coprecipitation Method for Preparing Cobalt Oxide (Co3O4) Catalyst to Efficiently Oxidize Ammonia

Abstract In this study three samples of cobalt oxide were prepared via coprecipitation at pH 9.5 using cobalt nitrate as a precursor. They were dried at 120°C before calcining at 400, 500, and 600°C. The crystalline phases were determined using X-ray diffraction (XRD), revealing the presence of the Co3O4 phase in all prepared samples in varying proportions. Fourier Transform Infrared Spectroscopy (FTIR) spectra showed distinct bands corresponding to the vibrational motion of the Co–O bond, confirming the formation of cobalt oxide (Co3O4). Scanning electron microscope (SEM) analysis of the Co 500 sample revealed particles in the range of 40–350 nm (average ~100 nm) with relatively low agglomeration, while energy-dispersive X-ray spectroscopy (EDX) confirmed a composition consistent with stoichiometric Co3O4 (85.7 wt % Co and 13.6 wt % O). Pyridine-adsorbed FTIR spectra indicated that the sample calcined at 500°C possessed the most balanced ratio of Lewis and Brønsted acid sites, which correlated with its highest catalytic activity. The textural properties of all samples were analyzed using nitrogen adsorption data at 77 K, and the adsorption isotherms were found to be type IV, with hysteresis loops indicating capillary condensation in mesopores. The specific surface area reached a maximum of 4.837 m2/g for the sample calcined at 500°C. This sample also exhibited the highest total acidity (0.035 mmol/g) and strong acidic sites (the initial electrode potential value Ei = 73.2 mV), which enhanced catalytic performance. Pore radius calculations further revealed that the samples contained mesopores. The catalytic efficiency of the prepared samples in the ammonia oxidation reaction was evaluated at 450°C. The sample calcined at 500°C demonstrated the highest catalytic activity. The sample calcined at 500°C achieved 100% NH3 conversion at 475°C and maintained full activity over 10 consecutive cycles, demonstrating high stability and reusability.