Low-temperature catalytic oxidation of ethanol over doped nickel phosphates

This work is focused on the synthesis and performance of Ni₃(PO₄)₂-based catalysts doped with Cu, Co, Mn, Ce, Zr, and Mg for the complete oxidation of ethanol, aiming at reducing emissions from ethanol-blended gasoline. Nickel phosphate was prepared via the co-precipitation method, followed by impregnation with the specified dopants. The catalysts were thoroughly characterized by XRD, N₂-physisorption, XRF, FTIR and Raman spectroscopy, FESEM, NH₃-TPD, CO₂-TPD, and H₂-TPR to explain their performance. All catalysts achieved complete ethanol conversion (100%) at a temperature below 320 °C. The performance of the catalysts was strongly influenced by the dopant type of which Co, Ce, Mn, and Mg showed high CO₂ selectivity (selectivity > 90% at 95% ethanol conversion temperature (T₉₅)). The mechanism of oxidation is affected by the acido-basicity of the catalysts and the redox properties leading to a reaction through ethylene formation over the acid catalysts and acetaldehyde over the basic catalysts. The redox properties of the doped catalysts play a crucial role in enhancing the catalytic activity and selectivity toward CO₂, as the redox-active dopants facilitate the activation of oxygen species, which are essential for the complete oxidation of ethanol. In particular, Co and Ce demonstrated superior redox characteristics, facilitating the conversion of intermediate species and leading to higher CO₂ selectivity while minimizing undesirable by-products.