Carbon-free hydrogen production via plasma-catalytic ammonia decomposition over transition metal-based catalysts: In situ probing by DRIFTS and SVUV-PIMS

The lack of comprehensive understanding of the reaction mechanism hinders the development of plasmacatalytic ammonia (NH3) decomposition as a potential route for producing carbon-free hydrogen. Herein, we investigated the reaction process over transition metal-based catalysts in a dielectric barrier discharge (DBD) reactor. For the first time, a combination of an integrated in situ diffuse reflectance infrared Fourier transform spectroscopy-DBD (in situ DRIFTS-DBD) and optical emission spectroscopy (OES) were applied to reveal that as for Ni/Al2O3, less NH3* was observed in the gas phase and more NH3 adsorbed on the surface. Combined with online synchrotron vacuum ultraviolet-photoionization mass spectrometry (SVUV-PIMS) it was further illustrated that N2 desorbed more quickly from Ni/Al2O3 than other tested catalysts. Additionally, compared with thermal catalysis, plasma further enhanced the adsorption of NH3 on Lewis acid sites and facilitated the desorption of N2. This study provided a better understanding of the plasma-catalytic NH3 decomposition reaction.