Although NH 3 has recently been regarded as a renewable and carbon-free energy source, NH 3 fuel has a high ignition temperature and its use results in the production of N 2 O/NO x . To overcome these issues, in this work, we focused on a novel catalytic combustion system and copper oxides (CuO x ) catalysts supported on aluminum silicates (Al 6 O 13 Si 2 , 3Al 2 O 3 ·2SiO 2 , 3A2S) and silicon oxides (SiO 2 ). The preparation methods for 3A2S as a support material were optimized to achieve high catalytic NH 3 combustion activity and high N 2 (low N 2 O/NO) selectivity. Because the CuO x supported on 3A2S prepared by an alkoxide method and subsequent calcination at 1200 °C for 5 h in air exhibited high catalytic performance for NH 3 combustion, the properties of the catalyst in addition to CuO x /SiO 2 thermally aged at 900 °C for 100 h in air were also evaluated using high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray mapping, operando X-ray absorption fine structure analysis, X-ray photoelectron spectroscopy, and gas adsorption techniques. Our findings suggest that the catalytic NH 3 combustion activity, NO selectivity, and N 2 O selectivity are closely associated with the reducibility (dispersion) of CuO x , local structures around Cu, fraction of the oxidation state (Cu2+), and adsorption species of NH 3 (NH, imide). Finally, we propose a reaction mechanism for catalytic NH 3 combustion over not only CuO x /3A2S but also CuO x /SiO 2 .