Microwave-assisted ammonia decomposition over metal nitride catalysts at low temperatures

Abstract

The negative environmental impact of fossil fuel-based energy systems has unveiled the need to develop a COx-free sustainable hydrogen (H2) economy. Employing a microwave-assisted route, a ternary metal nitride catalyst (i.e., Co2Mo3N), and a low-temperature-pressure NH3 decomposition process, this study investigated the possibility of developing a distributed H2 production process. This study not only explored lower cost-based catalyst systems but also the use of a microwave reactor to increase the energy efficiency of the process. Results from catalytic NH3 decomposition experiments, performed in microwave reactors on Co2Mo3N catalyst, demonstrated the peak energy efficiency (of ∼0.006 kgH2/kWh) at 400 °C in ambient pressure (with an NH3 conversion >90%) which was around ninety times (∼90 x) more efficient than a conventional system. Activation energy calculation also displayed a 20% less energy requirement for the microwave-based process (∼31 kJ mol−1) than the conventional system (∼37 kJ mol−1), indicating the advantage of the microwave-based process. Further microwave-assisted catalytic measurements and characterization of the Co2Mo3N catalyst, using x-ray diffraction (XRD) technique and scanning electron microscopic (SEM) images, revealed the excellent stability of this material at its peak performance (at 400 °C) and illustrated the potential of using this catalyst for a sustainable, economic, and energy-efficient approach for producing COx-free H2.