Supported binary CuOx–Pt catalysts with high activity and thermal stability for the combustion of NH3 as a carbon-free energy source

Abstract

Recently, NH₃ has been thought to be a renewable and carbon-free energy source. The use of NH₃ fuel, however, is hindered by its high ignition temperature and N₂O/NO production. To overcome these issues, in this study, the combustion of NH₃ over copper oxide (CuO_x) and platinum (Pt) catalysts supported on aluminium silicates (3Al₂O₃·2SiO₂), aluminium oxides (Al₂O₃), and silicon oxides (SiO₂) were compared. To achieve high catalytic activity for the combustion of NH₃ and high selectivity for N₂ (or low selectively for N₂O/NO), conditions for the preparation of impregnated binary catalysts were optimised. With respect to the binary catalysts, sequentially impregnated CuO_x/Pt/Al₂O₃ exhibited relatively higher activity, N₂ selectivity, and thermal stability. From XRD and XAFS analyses, CuO_x and Pt in CuO_x/Pt/Al₂O₃ were present as CuAl₂O₄ and metallic Pt, respectively. Given that the combustion activity was closely associated with the Pt nanoparticle size, which was estimated from the Scherrer equation and the pulsed CO technique, highly dispersed Pt nanoparticles were crucial for the low-temperature light-off of NH₃. For single and binary catalysts, although NH (imide) deformation modes as a key species for N₂O production were detected by in situ FTIR spectral analysis, the band intensity of CuO_x/Pt/Al₂O₃ was less than those of CuO_x/Al₂O₃ and Pt/Al₂O₃. Therefore, CuO_x/Pt/Al₂O₃ exhibits high selectivity for N₂ in NH₃ combustion.