3D-printed zeolite 13X-Strontium chloride units as ammonia carriers.

The selective catalytic reduction (SCR) system in automobiles using urea solution as a source of NH suffers from solid deposit problems in pipelines and poor efficiency during engine startup. Although direct use of high pressure NH is restricted due to safety concerns, which can be overcome by using solid sorbents as NH carrier. Strontium chloride (SrCl) is considered the best sorbent due to its high sorption capacity; however, challenges are associated with the processing of stable engineering structures due to extraordinary volume expansion during the NH sorption. This study reports the fabrication of a novel structure consisting of a zeolite cage enclosing the SrCl pellet (SPZC) through extrusion-based 3D printing (Direct Ink Writing). The printed SPZC structure demonstrated steady sorption of NH for 10 consecutive cycles without significant uptake capacity and structural integrity loss. Furthermore, the structure exhibited improved sorption and desorption kinetics than pure SrCl. The synergistic effect of zeolite as physisorbent and SrCl as chemisorbent in the novel composite structure enabled the low-pressure (<0.4 bar) and high-pressure (>0.4 bar) NH sorption, compared to pure SrCl which absorbed NH at pressures above 0.4 bar. Regeneration of SPZC composite sorbent under evacuation showed that 87.5% percent of NH was desorbed at 20 °C. Thus, the results demonstrate that the rationally designed novel SPZC structure offers safe and efficient storage of NH in the SCR system and other applications.