Experimental and theoretical investigation of the Na+ → Li+ cation exchange in mordenite and its effect on CO2 adsorption properties

Abstract

Anthropogenic CO2 emissions are the major drivers of global warming and climate change. The adsorption of CO2 is one of the strategies to mitigate these emissions. In this sense, different materials have been used as adsorbents as is the case of zeolites. In this work,experimental infrared and X-ray analyses together with DFT (Density Functional Theory)theoretical calculations were employed to study the adsorption of CO2 on mordenite zeolites (Na-MOR). Ion exchange followed by chemical analysis showed that the Na+ of Na-MOR was not completely substituted under the experimental conditions employed. The XRD (X-ray Diffraction) analysis indicated that Na+ exchanged for Li+ did not affect the crystallinity of the materials. The infrared results showed that CO2 interacted linearly with the sodium and lithium cations present in the main channel of the mordenite framework. Sodium in dry samples favored the formation of carbonates and hydroxycarbonate species, as did the presence of low water content in the LixNa-MOR. The DFT periodical calculation of dehydrated mordenite models led to CO2 adsorption energies in the range of − 31.6 to − 34.2 kJ mol−1, with the highest adsorption energy found for sodium mordenite.The asymmetric stretching ν3 (CO2) vibration mode resulted intense and presented a shift which indicated a higher CO2 interaction of Na-MOR. The presence of some water molecules in the mordenite framework caused a decrease in the adsorption energy.