Reducing emissions of NO_x from internal combustion engines is crucial for improving air quality and
meeting regulatory standards. One effective method is selective catalytic reduction (SCR), which uses NH₃
as a reducing agent over a suitable catalyst to convert NO_x to N_x and H₂O. However, the use of NH₃ presents
significant safety risks when stored in pressurized vessels, so commercial SCR units typically employ urea as
a reducing agent, which produces CO2 as a byproduct. Alternatively, alkali earth metal halides (AEMHs)
offer a solid-state storage solution, but the volumetric expansion associated with the formation of ammine
complexes limits their practicality.
Here, we propose a novel approach for shaping SrCl₂ into a structured sorbent for NH₃ storage in SCR units
using Direct Ink Writing (DIW) of SrCl₂ -bentonite slurries. The 3D-printed component's porous lattice design
improves NH₃ access to the salt and accommodates SrCl₂ 's volumetric expansion (over 400%) to preserve
structural integrity. The use of bentonite allows for good mechanical properties of the printed monoliths
after drying without the need for heat treatments, which can be problematic due to the poor stability of
SrCl₂ at high temperature. Our SrCl₂ -bentonite monoliths exhibited comparable NH₃ storage capacity to that
of pure SrCl₂ and maintained performance and structural integrity during numerous absorption-desorption
cycles.
In summary, our approach offers a safer and more efficient method for NH₃ storage in SCR units and
demonstrates the potential of additive manufacturing for creating novel sorbent materials.