Viability of Boron Nitride Nanotubes as a Support Structure for Metal Nanoparticle Catalysts for the Plasma-Catalytic Synthesis of Ammonia

Abstract

Nonthermal plasma-catalytic processes are being investigated as an alternative method to the energy-intensive and environmentally impactful Haber-Bosch (H-B) process for ammonia synthesis. Due to the large-scale production of this commodity chemical, the H-B process uses 1-2% of the world's energy, 3-5% of the world's refined natural gas and corresponding CO2 emissions. With the recent development of large-scale electrolysers for H2 production powered by renewable electricity, the integration of a plasma process at scale may be the last step toward the all-electric and environment-friendly green ammonia synthesis. However, the most encouraging results are still an order of magnitude below the H-B process in terms of energy efficiency. Key to success are the nanocatalysts, the plasma excitation and gas mixing, with reaction kinetics as the coupling between these variables. Boron nitride nanotubes (BNNTs) are a dielectric material with high chemical and thermal stability, and a unique affinity to ammonia. These properties make them interesting substrates for nanocatalysts. We report on the surface modification of BNNTs and the deposition of metal catalyst nanoparticles by two sequential plasma processing steps; plasma functionalization and pulsed laser ablation to produce BNNT-supported nanoparticle catalysts. We also report our additional findings on the morphology, activity, and stability of the produced catalysts.