CFD-guided catalytic combustion optimization of CH4/H2/NH3 blends using staged Ni-based catalysts: Insights into NOx mitigation and efficiency enhancement

Abstract

The decarbonization of industrial combustion systems demands fuel strategies that reduce greenhouse gas emissions while maintaining high efficiency and operational stability. This study explores the catalytic combustion behavior of ternary CH₄/H₂/NH₃ fuel blends using high-fidelity Large Eddy Simulation (LES) integrated with a validated reduced chemical mechanism (51 species, 420 reactions). The focus is to overcome ammonia's inherent limitations: low reactivity, high ignition temperature (> 650 °C), and elevated NO_x formation, by leveraging catalytic surface interactions. A novel staged catalyst configuration based on Ni-Cu/Fe₂O₃ is proposed, with upstream NH₃ decomposition and downstream NO_x reduction zones. Parametric simulations reveal that a 30:30:40 volumetric fuel blend (CH₄:H₂:NH₃) achieves optimal performance, yielding combustion efficiency above 97 %, NO_x emissions below 30 ppm, and NH₃ slip under 15 ppm. Catalyst staging improves performance over uniform coating, reducing NO_x by 79.3 % and NH₃ slip by 56.1 %. Stability maps indicate extended flame anchoring over a wide equivalence ratio range (0.65–1.1) and inlet velocities up to 25 m/s. A comprehensive reaction pathway analysis attributes 65 % of NO_x to fuel NO, 25 % to thermal NO, and 10 % to prompt NO mechanisms. Catalytic activity proves most effective within the 550–650 K surface temperature window. The results highlight a scalable pathway for integrating catalytic combustion in low-carbon energy systems and establish a foundation for future experimental validation. This work offers practical insight for transitioning toward cleaner combustion technologies, particularly in ammonia-assisted hybrid fuels for advanced burners, reformers, and industrial heating applications.