Calcium/strontium chloride impregnated zeolite A and X granules as optimized ammonia sorbents

Abstract

Calcium chloride (CaCl₂) impregnated zeolite A and strontium chloride (SrCl₂) impregnated zeolite A and X composite granules were evaluated as ammonia sorbents for automotive selective catalytic reduction systems. The SrCl₂-impregnated zeolite A granules showed a 14% increase in ammonia uptake capacity (8.39 mmol g⁻¹) compared to zeolite A granules (7.38 mmol g⁻¹). Furthermore, composite granules showed 243% faster kinetics of ammonia sorption (0.24 mmol g⁻¹ min⁻¹) compared to SrCl₂ (0.07 mmol g⁻¹ min⁻¹) in the first 20 min. The composite CaCl₂/SrCl₂ impregnated zeolite A granules combined the advantages of the zeolites and CaCl₂/SrCl₂, where the rapid physisorption from zeolites can reduce the ammonia loading and release time, and chemisorption from the CaCl₂/SrCl₂ offers abundant ammonia capacity. Moreover, by optimizing the content of SrCl₂ loading, the composite granules maintained the granular form with a crushing load of 17 N per granule after ammonia sorption–desorption cycles. Such structurally stable composite sorbents offer an opportunity for fast ammonia loading/release in automotive selective catalytic reduction systems.