Structure-performance relationships of magnesium-based CO2 adsorbents prepared with different methods

Abstract

Magnesium-based adsorbents present great potential in separating CO2 from flue gas stream. To satisfy the requirement of efficient CO2 capture, it is imperative to select suitable methods for preparing MgO adsorbents with good physicochemical properties. In this study, MgO adsorbents were prepared with different methods using MgCl2·6H2O as magnesium precursor, and the effect of synthesis method on their structure-performance relationships were investigated. It is found that MgO adsorbents prepared with different methods exhibited varied physicochemical properties, and these were associated with their diverse CO2 adsorption capacities. Amongst the different MgO adsorbents, the sample prepared with the solid-state chemical reaction method (MgO-SR) featured good textural properties (high specific surface area and total pore volume of 100.03 m2/g and 0.67 cm3/g), preferable surface morphology (sheet-like structure with reduced layer diffusion resistance) and excellent CO2 adsorption capacity (2.39 mmol CO2/g). The solid-state chemical reaction method endowed the adsorbent with abundant surface basic active sites, and CO2 molecules interacted with the weak sites (OH group), medium sites (Mg-O pairs) and strong sites (O2−) to form stable bicarbonate, bidentate and unidentate carbonates. The experimental CO2 uptakes were in good agreement with the values predicted by the Avrami fractional kinetic model. Physical adsorption and chemisorption coexisted in the CO2 adsorption process and the chemisorption sites played a dominant role. The approach enlightens the facile fabrication of cost-effective MgO adsorbents from waste precursors for large-scale CO2 capture applications.