Efficient removal of hydrogen sulfide (H₂S) while utilizing its H content to produce hydrogen (H₂) has been a sought-after technology in the industry. The two most common technologies for abatement of H₂S – Claus process and reactive adsorption, produce steam (H₂O) instead of H₂and suffer from issues such as unfavorable thermodynamics, poor recyclability of adsorbents, and requirement of air separation unit (ASU), thereby necessitating the development of a new technology. In this work, a cyclic redox scheme utilizing nickel sulfide (Ni₃S₂) impregnated on a support as a catalytic sulfur carrier was established. The carrier effectively reacts with H₂S to form NiS, while generating hydrogen (H₂). Furthermore, the sulfided carrier is fully regenerated using carbon dioxide (CO₂) with preferable formation of sulfur (S₂), alleviating the need for an ASU. Zirconium oxide (ZrO₂) and magnesium aluminate (MgAl₂O₄) have been used as supports to provide effective dispersion of the active metal sulfide and overcome the thermal instability of Ni₃S₂. Redox cycles performed using thermogravimetric analyzer show that Ni₃S₂impregnated on both supports exhibit stable reactivity over 10 continuous cycles. Moreover, Ni₃S₂ impregnated on ZrO₂ showcased nearly 100% improvement over MgAl₂O₄. Results from density functional theory calculations reveal that MgAl₂O₄ acts as an inert support, while ZrO₂ serves as a bi-functional catalytic support that increases the surface area and participates in H₂S decomposition. Furthermore, H₂S decomposition on ZrO₂ was found to undergo a non-oxidative route with S₂ and H₂ as the main products, wherein S₂ was found to be adsorbed onto the Ni₃S₂ surface, further sulfidizing it to promote the overall sulfidation kinetics. Fixed bed studies and various solid characterization were performed to further analyze the solid phase and surface characteristics and corroborate the results. The findings from this study can be leveraged to develop an economically attractive and environmentally sustainable process.

Ashin Sunny

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