Local Structures and Catalytic Ammonia Combustion Properties of Copper Oxides and Silver Supported on Aluminum Oxides

The local structures and catalytic NH3 combustion properties of copper oxides (CuOx) and silver (Ag) catalysts supported on aluminum oxides (Al2O3) were studied. In order to achieve high catalytic NH3 combustion activity and high N2 (low N2O/NO) selectivity, the preparation conditions for impregnated binary catalysts were optimized. In comparison with the single CuOx/Al2O3 and Ag/Al2O3, binary CuOx–Ag supported on Al2O3 showed high performance for catalytic NH3 combustion. Among the binary catalysts, sequentially impregnated CuOx/Ag/Al2O3 exhibited the highest activity and N2 selectivity. Because the combustion activity is closely associated with the Ag–Ag coordination number estimated from Ag K-edge XAFS, highly dispersed Ag nanoparticles supported on Al2O3 are considered to play a key role in the low-temperature light-off of NH3. CuOx/Ag/Al2O3 also showed higher N2 (lower NO) selectivity for temperatures at which NH3 conversion reached approximately 100%, indicating that the N2 is directly produced from the NH3 combustion reaction over CuOx/Ag/Al2O3. Based on several analyses, a reaction mechanism for catalytic NH3 combustion over CuOx/Ag/Al2O3 was finally suggested.