Enhancing CO2 Adsorption and Separation Properties of Aluminophosphate Zeolites by Isomorphous Heteroatom Substitutions.

Mg, Co-substituted aluminophosphate zeolites with ERI framework topology (denoted as MgAPO-ERI and CoAPO-ERI) have been synthesized under hydrothermal conditions by using N, N, N', N'-tetramethyl-1,6-hexanediamine as organic template. Their CO2 adsorption properties are investigated in comparison to those of the pure aluminophosphate counterpart AlPO-ERI. CoAPO-ERI shows the highest CO2 uptake of 57.3 cm3 g-1 (273 K and 1 bar) and the highest isosteric heat of 39.0 kJ mol-1 among the three samples. Importantly, the incorporation of Mg2+ and Co2+ ions in the framework of AlPO-ERI can greatly improve the adsorption selectivities of CO2 over CH4 and N2. Whereafter, transient breakthrough simulations were investigated and further proved the advantages of heteroatoms for separations. These results demonstrate that isomorphous heteroatom substitutions in aluminophosphate zeolites play a key role in enhancing CO2 adsorption and separation abilities.