Supported binary CuOx–Pt catalysts with high activity and thermal stability for the combustion of NH3 as a carbon-free energy source†
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 (CuOx) 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 CuOx/Pt/Al2O3 exhibited relatively higher activity, N2 selectivity, and thermal stability. From XRD and XAFS analyses, CuOx and Pt in CuOx/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 CuOx/Pt/Al2O3 was less than those of CuOx/Al2O3 and Pt/Al2O3. Therefore, CuOx/Pt/Al2O3 exhibits high selectivity for N2 in NH3 combustion.