On the impact of copper local environment on hydrogen sulfide adsorption within microporous AlPO₄-5

This work aims at elucidating the most active modes of copper incorporation towards H2S adsorption. Various synthesis methodologies were followed, notably, incorporation via isomorphic substitution, liquid ion exchange (LIE), vapor phase ion exchange (VIE), and nanoparticles inclusion during hydrothermal synthesis, for the introduction of copper into AlPO4-5 and SAPO-5. Techniques such as XRD and SEM/EDX, TEM, FT-IR and N2 adsorption-desorption were employed to characterize the synthesized materials. The Cu- containing materials were examined as sorbents for H2S removal via breakthrough experiments at 150 °C. The highest sulfur removal capacity was attained over the CuO nanoparticles supported in AlPO4-5 (10 % CuO/AlPO4-5), followed by a copper-based material prepared by VIE (Cu-VIE-0.2), accounting for H2S breakthrough capacities of 0.31 and 0.17 mmol g-1, respectively. The superior performance of these two materials could be ascribed to the relatively higher copper loading in the form of CuO as confirmed by XRD. Comparing the capacity per gram of active site, it was revealed that positioning Cu ions in extra-framework sites leads to an order of magnitude enhancement. This can be attributed to the possibility of a Cu ion to interact with more than one H2S molecule simultaneously unlike the other incorporation modes examined. Furthermore, copper ions incorporated into the crystal framework were found to be inactive towards H2S adsorption.