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 NH₃ suffers from solid deposit problems in pipelines and poor efficiency during engine startup. Although direct use of high pressure NH₃ is restricted due to safety concerns, which can be overcome by using solid sorbents as NH₃ carrier. Strontium chloride (SrCl₂) 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 NH₃ sorption. This study reports the fabrication of a novel structure consisting of a zeolite cage enclosing the SrCl₂ pellet (SPZC) through extrusion-based 3D printing (Direct Ink Writing). The printed SPZC structure demonstrated steady sorption of NH₃ for 10 consecutive cycles without significant uptake capacity and structural integrity loss. Furthermore, the structure exhibited improved sorption and desorption kinetics than pure SrCl₂. The synergistic effect of zeolite as physisorbent and SrCl₂ as chemisorbent in the novel composite structure enabled the low-pressure (<0.4 bar) and high-pressure (>0.4 bar) NH₃ sorption, compared to pure SrCl_2, which absorbed NH₃ at pressures above 0.4 bar. Regeneration of SPZC composite sorbent under evacuation showed that 87.5% percent of NH₃ was desorbed at 20 °C. Thus, the results demonstrate that the rationally designed novel SPZC structure offers safe and efficient storage of NH₃ in the SCR system and other applications.