Fuel-Rich Ammonia Catalytic Combustion on Gadolinium-Doped Ceria (GDC) Supported Copper Oxide Catalyst

Abstract

Ammonia combustion faces challenges such as high ignition temperature, low flame speed, and potential NO_x emissions. Catalytic combustion offers an alternative solution to burn ammonia with high efficiency while minimizing NO_x formation. This study aims to develop a fuel-rich, catalytically stabilized ammonia combustion and study the reactivity and NO_x formation of a novel gadolinium-doped ceria (GDC) supported CuO catalyst (CuO/GDC). The CuO/GDC catalyst was synthesized using the wet impregnation method and characterized using physisorption, X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), and Transmission Electron Microscopy (TEM). Its performance was tested in a fixed-bed reactor and compared to CuO/γ-Al₂O₃, with an equivalence ratio (ER) of 1.5 and temperatures ranging from 100°C to 800°C. The reaction mechanism of ammonia combustion over CuO/GDC was investigated with X-ray photoelectron spectroscopy (XPS) analysis and microkinetic modeling integrated with Density Functional Theory calculations. The CuO/GDC catalyst demonstrated a high NH₃ conversion of 100% with a great N₂ selectivity of over 99% at 800°C and minimal NO_x formation, which was attributed to the strong adsorption of N and O species on its surface and mitigation of nitrogen oxide formation. Apart from altering the overall adsorptive properties of the catalyst, the mixed ionic-electronic conductivity of GDC also facilitates oxygen ion transport on the catalyst surface, promoting redox-driven catalytic activity. These findings highlight the potential of the use of mixed conductor as an effective catalyst support for fuel-rich ammonia catalytic combustion.