| Summary: | <p>Ammonia sorbents are important for both the synthesis and transport of so-called green ammonia. Though MgCl<sub>2</sub> is currently the most commonly used absorbent for ammonia it has a number of deficiencies and so new materials are needed targeting fast sorption and desorption speed and high temperature and cycling stability. </p>
<p>13X zeolites underwent ion exchange and were studied for ammonia adsorption. The sodium ions in the 13X structure were replaced by protons, magnesium or lanthanum ions. In each case, the ammonia capacity was increased by the ion exchange, most significantly for magnesium, with fast, stable adsorption. Protons generated strong Brønsted acid sites which gave ammonia that was stable at high temperatures, lanthanum generated Lewis acid sites which gave weakly bound ammonia stable only at low temperatures and magnesium generated a combination of strong Brønsted acid and weak Lewis acid sites giving low and high temperature ammonia. In each material the locations of the ammonia binding sites were identified using SXRD, supported by modelling.</p>
<p>Lanthanum ion exchange was shown to cause structural disruption due to the size of the lanthanum ions. This disruption was shown to be related to lanthanum content but detrimental to capacity. The acidity of the lanthanum zeolites could be tuned using varying lanthanum content.</p>
<p>A variety of layered materials, including MgCl<sub>2</sub>, were studied in greater detail. Treatment of MgCl<sub>2</sub> using acetone was found to significantly improve the absorption rate at detriment to the ammonia capacity; this was proposed to be due to reordering of exfoliated MgCl<sub>2</sub> layers or nanopore generation. This treatment was found to be unstable with both time and cycling and attempted alternative methods of stable layer disruption were unsuccessful. Instead, layers were exfoliated and supported on zeolite which gave fast, stable sorption even at high temperatures and low pressures.</p>
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