Catalytic conversion to ammonia through solid-state nitrate as a proposal for the emerging usage of nitrogen oxides

Abstract

Nitrogen oxides, NOx, that arise anthropogenically from combustion at high temperature using air are serious byproducts that cause air pollution. Here, we propose a catalytic conversion system by alternate switching of inlet gas from NOx containing O₂-rich combustion gas (e.g., 1000 ppm NO + 10% O₂) to NO/O₂-free reduction one (e.g., 1% H₂). According to this gas-switching operation, solid-state nitrate, stored with alkali earth metal species, was converted to gaseous NH₃ under ambient pressure, which would possibly be useful for solving the nitrogen crisis as well as constructing a new industrial structure of a circular nitrogen economy. Large Pt nanoparticles inside mesoporous alumina particles, created by an aerosol-assisted one-pot synthesis with Pt sources followed by calcination at high temperature (e.g., 850 °C), were helpful for shifting the efficient-working temperature to a higher region. A Ba/Pt@mAl₂O₃(γ) type nanocomposite catalyst worked very well at 250 °C and higher. Selectivity for NH₃ reached 90%, and was also achieved using Ca/Pt@mAl₂O₃(γ), without a high-energy process like the cleavage of N₂.