Performance of copper-aluminum catalysts impregnated with potassium in NO and N2O reduction by CO

Abstract

Three-way automotive catalysts (TWC) are based on noble metals and have two significant limitations: high cost and tendency to form, at low temperatures, nitrous oxide (N₂O), which contributes to the greenhouse effect and ozone layer depletion. Thus, it is crucial to study possible substitutes for these components. In this work, catalysts prepared from copper and aluminum hydrotalcite-like materials impregnated with potassium were studied. The formation of the hydrotalcite phase and CuO phase in the catalyst was evidenced by X-ray diffraction (XRD). Temperature-programmed reduction (TPR) results showed that the alkali metal positively influences the reducibility of the catalyst, decreasing its reduction temperature. Temperature-programmed desorption (TPD) analysis revealed electronic promotion, confirming that the presence of potassium facilitates the desorption of molecular nitrogen from the surface and decreases that of N₂O. Catalytic tests showed differences in the behavior of the catalysts depending on the pretreatment performed, suggesting that the interaction between potassium and oxidized or reduced copper gives rise to different catalytic sites. The formation of oxygen vacancies in potassium-containing catalysts, identified by XPS, and the increase in the copper metal surface area contributed to explaining the better performance of these catalysts. Also, based on the catalytic tests, more selective catalysts with the addition of potassium (minimizing N₂O formation) were obtained, especially at a ratio of 0.025 K/Cu (mol/mol) and after a reducing pretreatment. This catalyst also showed 100 % N₂O conversion in the reduction by CO at temperatures close to 100 °C, confirming its excellent performance in nitrous oxide abatement.