Examining the impact of different anions in Cu precursors on sulfur adsorption through zeolites with Cu ion-exchange

The majority of hydrogen is generated by converting hydrocarbons, with natural gas reforming accounting for over 50% of the total hydrogen production. However, the utilization of natural gas in generating hydrogen causes catalyst deactivation during the reforming process because of presence of sulfur compounds as odorants in commercial natural gas. Therefore, the removal of sulfur compounds from natural gas should be prioritized before its application in hydrogen production. Adsorption using Cu-ion-exchanged zeolites is an effective method for removing sulfur compounds from natural gas. In this study, the adsorptive desulfurization performance of tetrahydrothiophene (THT) was evaluated using pristine NaY and Cu-ion-exchanged Y zeolites. In particular, the effects of anions in the Cu compounds used for the ion exchange of zeolites were investigated using three Cu precursors (Cu(NO₃)₂, Cu(Ac)₂, and CuSO₄). Among the tested zeolite adsorbents, the NaY zeolite ion-exchanged with Cu(Ac)₂ exhibited the highest adsorption uptake, whereas the NaY zeolite ion-exchanged with CuSO₄ demonstrated the lowest adsorption uptake for THT. The analytical results indicated that following the exchange of Cu ions, a rearrangement of Si and Al was observed within the zeolite framework, resulting in the Si site distribution. The rearrangement of the framework and distribution of Si sites was influenced by the anions present in the Cu precursors. In addition, it was observed that Cu²⁺ primarily occupied two locations within the zeolite, namely the supercage and the sodalite cage, and the distribution of Cu²⁺ between these two sites varied amongst the Cu-ion-exchanged zeolites. This discrepancy was linked to the adsorption uptake for THT.