Ammonia Combustion Properties of Copper Oxides-based Honeycomb and Granular Catalysts

Although NH3 has been recently regarded as a renewable and/or carbon-free energy source, the use of NH3 fuel is hindered by its high ignition temperature and N2O/NO production. To overcome these problems, catalytic NH3 combustion systems and novel powder (granule) catalysts that showed high activity and low N2O/NO selectivity were previously developed. In this study, we extended our research to investigate the NH3 combustion properties of copper oxides (CuOx)-based honeycomb catalysts (CuOx/Al2O3, CuOx/10Al2O3 · 2B2O3, CuOx/Ag/Al2O3, CuOx/Pt/Al2O3, and so on) for practical applications. Therefore, several monolithic honeycomb catalysts were prepared and their reaction properties were evaluated and compared with those of granular catalysts. The spatial distribution in coated honeycombs before and after thermal aging was examined by the X-ray line analysis technique, which suggested that supported catalysts (thickness of the layers: ca. 100 μm) had homogeneously dispersed CuOx and/or Pt in each catalyst. NH3 combustion properties (activities and selectivities) for honeycomb catalysts were similar to those of the granular catalysts, indicating that their properties were typically independent from the shape of the catalysts. Spectra from X-ray photoelectron spectroscopy were obtained to estimate the fraction of Cu2+/Cu+ for the honeycomb catalysts of CuOx/10Al2O3 · 2B2O3. By density functional theory computations, it was suggested that highly dispersed Ag nanoparticles show a high activity.