Removal of H 2 S to produce hydrogen in the presence of CO on a transition metal-doped ZSM-12 catalyst: a DFT mechanistic study.

Hydrogen sulfide (H ₂ S) leads to corrosion in transport lines and poisoning of many catalysts. Meanwhile, H ₂ S is an inexhaustible potential source of hydrogen, which is a very valuable chemical reagent and an environmentally friendly energy product. Therefore, removal of H ₂ S and producing hydrogen gas using potential catalysts has been intensively studied, according to the equation: H ₂ S(g) + CO(g) → COS(g) + H ₂ (g). In this study, hydrogen sulfide (H ₂ S) decomposition in the presence of CO over transition metal-doped ZSM-12 clusters (TM-ZSM-12) has been investigated based on DFT calculations at the B3LYP-D3/6-31G(d,p) level. The calculation results reveal that the proposed reaction mechanism is controlled by 4 key steps, (i) hydrogen dissociation (E _a1 = +0.04 eV for the 1st hydrogen and E _a2 = +0.22 eV for the 2nd hydrogen), (ii) COS desorption (the rate-determining step of this H ₂ S removal process, E _des = +1.18 eV), (iii) hydrogen diffusion to the transition metal with an energy barrier (E _a3 ) of +0.62 eV, and (iv) the H ₂ formation step (E _a4 = +0.94 eV). Our results indicate that in the presence of CO, the Cu-ZSM-12 cluster has a potential application as a highly active catalyst for H ₂ S removal together with hydrogen production.