(406g) Zeolite-Calcium Chloride Composites As Rapid Ammonia Carriers

Ammonia (NH₃) is a versatile material utilized in various applications, yet with corrosive, toxic and hazardous nature. A stable, reliable ammonia carrier, therefore, is of desire for expanding the potential ammonia applications, such as clean fuel, reductant in the automotive selective catalytic reduction (SCR) system. Particularly in the SCR system, conventional urea solution as an ammonia carrier generates CO₂ as byproduct and requires high energy for ammonia production. Alkaline earth metal halides (AEMHs) as ammonia carrier are promising in solid state due to high ammonia uptake capacity and offer possibilities to structure in macroscopic shapes with other materials to improve the uptake and release kinetics.

CaA (Linde Type A) zeolite can be conveniently structured into granules and pellets. The structured zeolite provides a rapid ammonia adsorption kinetics at low pressure (below 0.4 bar). The ammonia uptake capacity of 5A zeolite is relatively low (7.4 mmol/g at 1 bar, room temperature). Herein, we report zeolite-calcium chloride (CaCl₂) composites, which combine the physical adsorption and chemical absorption of ammonia. With facile freeze granulation and salts impregnation method, the zeolite-CaCl₂ composites are feasible for structuring with a wide flexibility in zeolite loading. The ammonia uptake capacity is elevated to 13.0 mmol/g (76% more, compared with raw 5A) by adding 10 wt% CaCl₂, which has almost no volume change in the granules. Moreover, the rapid kinetics maintains in the low-pressure regime, which can prevent the nitrogen oxides (NO_x) escape from the SCR reaction and enhance the NO_x reduction (deNOx) efficiency.