Mesoporogen-free synthesis of hierarchical zeolite A for CO2 capture: Effect of freeze drying on surface structure, porosity and particle size

Zeolite A is one of the admirable adsorbent used for CO2 adsorption. Intrinsically microporous zeolite A has the significant drawback of lower mass transfer rate and pore blockage even after functional modification. The development of hierarchical zeolite A can overcome these limitations by offering additional levels of pores. In this study, we developed hierarchical zeolite A with highly porous structure using an environmentally benign approach, i.e. hydrothermal followed by freezing-drying. This soft templating approach is economic and eliminates the use of eco-unfriendly organic templates or mesoporogen. The impact of freeze-drying (FDZA) on the development of hierarchical zeolite A was studied and compared with the traditional oven-drying (ODZA). The influence of freeze drying on the pore characteristics, crystallinity, and morphology of hierarchical zeolite A was explored. Better mass transfer rates and an 8% increase in carbon dioxide adsorption were achieved for FDZA compared to ODZA due to the increased porosity, surface area, and relatively lesser particle size. This study pointed to the freeze-drying as a novel approach for developing hierarchical pores in zeolite A.