Effect of copper introduction via wet-impregnation on the performance of Mg-Al mixed metal oxides in selective ammonia oxidation

This study investigates catalytic efficiency of Cu-impregnated Mg-Al hydrotalcite-derived mixed metal oxides as selective ammonia oxidation (NH 3 -SCO) catalysts. Copper was introduced via wet impregnation method onto calcined Mg-Al oxides followed by recalcination at 600 and 800 °C. Cu loading was in range 5–15 wt% to determine the loading effect. Obtained materials were characterized by several techniques (X-ray diffraction, low temperature nitrogen physisorption or temperature programmed reduction) and tested as catalysts of NH 3 -SCO. The study revealed that catalytic activity and selectivity are significantly influenced by copper loading and its surface accessibility rather than calcination temperature. Obtained results highlighted crucial role of dispersed, non-isolated, CuO species in selective and efficient NH 3 oxidation. The formation of bulk-like species led to unselective oxidation and formation of side products, while presence of isolated CuO species lowers the activity. The characterisation results together with catalytic tests show that enhancing copper accessibility and reducibility on the materials surface result in better catalytic efficiency. The materials impregnation allows greater surface exposure of active copper species compared to materials where Cu was introduced during parent hydrotalcite co-precipitation. Results suggest that use of well-developed surface area support allow copper loading increase without formation of undesired bulk-like species.