Insights into the Oxygen Vacancy Filling Mechanism in CuO/CeO2 Catalysts: A Key Step Toward High Selectivity in Preferential CO Oxidation

Reduction and Oxidation of Cu Species in Cu-Faujasites Studied by IR Spectroscopy

The process of reduction (by hydrogen and ethanol) and oxidation (by oxygen and NO) of Cu sites in dealuminated faujasite-type zeolites (of Si/Al = 31) was studied by infrared (IR) spectroscopy with CO (for Cu⁺) and NO (for Cu²⁺) as probe molecules. Two zeolites were studied: one of them contained mostly Cu⁺_exch., whereas another one contained mostly Cu²⁺ and Cu⁺_ox. The susceptibility of various forms of Cu for reduction were investigated. IR experiments of CO sorption evidenced that Cu⁺_ox. was more prone for the reduction than Cu⁺_exch. According to NO sorption studies, Cu²⁺_exch. was reduced in the first order before Cu²⁺_ox. Ethanol reduced mostly Cu²⁺ and, also, some amounts of Cu⁺. The treatment with oxygen caused the oxidation of Cu⁺ (both Cu⁺_exch. and Cu⁺_ox.) to Cu²⁺. The adsorption of NO at 190K produced Cu⁺(NO)₂ dinitrosyls, but heating to room temperature transformed dinitrosyls to mononitrosyls and increased the Cu²⁺ content.

Highly Efficient CuO/α-MnO2 Catalyst for Low-Temperature CO Oxidation

Copper manganese composite (hopcalite) catalyst has been widely explored for low-temperature CO oxidation reactions. However, the previous reports on the stabilization of such composite catalysts have shown that they deactivated severely under moist conditions. Herein, we developed an α-MnO₂ nanorod-supported copper oxide catalyst that is very active and stable for the conditions with or without moisture by the deposition precipitation (DP) method. Incredibly, the CuO/MnO₂ DP catalyst (with 5 wt % copper loading) achieves superior activity with a reaction rate of 9.472 μmol^-1·g_cat^-1·s^-1 even at ambient temperatures, which is at least double times of that for the reported copper-based catalyst. Additionally, the CuO/MnO₂ DP catalyst is significantly more stable than the copper manganese composite catalysts reported in the literature under the presence of 3% water vapor as well as without moisture. A correlation between the catalytic CO oxidation activity and textural characteristics was derived via multitechnique analyses. The results imply that the superior activity of the CuO/MnO₂ DP catalyst is associated with the proper adsorption of CO on partially reduced copper oxide as Cu(I)-CO and more surface oxygen species at the interfacial site of the catalyst.