Delafossite Ag₂CuMnO₄ is a Novel Catalytic Material for Low‐Temperature Oxidation of CO and NH₃

Abstract

Ternary oxide of silver, copper, and manganese (Ag2CuMnO4) was prepared by hydrothermal synthesis in an alkaline solution. The prepared sample was characterized by a delafossite crystal structure without any other crystallized phases. The catalytic properties of Ag2CuMnO4 in oxidation reactions using molecular oxygen were investigated. High catalytic activity was found for Ag2CuMnO4 in the CO oxidation at room temperature, while ammonia oxidation occurred above 100 °C. Ammonia oxidation resulted in the formation of N2O/N2 or NO/NO2 products depending on the reaction temperature. As a result of the reaction exposure on Ag2CuMnO4 during heating up to 400 °C, a modification of surface composition with preservation of the delafossite structure was found. Oxide Ag2CuMnO4 was shown to be operating in wet CO oxidation under ambient conditions. Obtained data emphasize that Ag2CuMnO4 can be considered as a novel and prospective catalytic material with a high potential of application for oxidation processes at low temperatures including ambient conditions.

Unraveling the Structure–Activity Relationship of Delafossite Ag2CuMnO4 in CO Oxidation at Subambient Temperatures

“…For the preparation of Ag 2 CuMnO 4 , an original procedure of hydrothermal synthesis was used, as described previously. 16 The precursors such as Mn(NO 3 ) 2 , Cu(NO 3 ) 2 , and AgNO 3 in a stoichiometric ratio were dissolved in 40 mL of distilled water. 40 mL of NaOH solution with an excess of Na 2 S 2 O 8 was added to the metal nitrate solution so that the final pH value exceeded 12.…”

“…For the preparation of Ag 2 CuMnO 4 , an original procedure of hydrothermal synthesis was used, as described previously . The precursors such as Mn­(NO 3 ) 2 , Cu­(NO 3 ) 2 , and AgNO 3 in a stoichiometric ratio were dissolved in 40 mL of distilled water.…”

“…Catalysts operating the low-temperature CO oxidation under humid conditions usually contain noble metals, such as gold or palladium. − However, we have recently shown that the ternary oxide of silver, copper, and manganese (Ag 2 CuMnO 4 ) with a delafossite structure also exhibits activity in the wet oxidation of CO at room temperature . As in the case of the hopcalite catalyst, the low-temperature activity of the ternary oxide is likely due to the presence of a Cu–Mn pair with high charge lability. , Pretreatment of the ternary oxide in a CO + O 2 mixture was found to cause changes in the surface states of copper and manganese and their quantitative ratio.…”