Selective Catalytic Oxidation of H₂S over Well-Mixed Oxides Derived from Mg₂Al_<i>x</i>V_1–<i>x</i> Layered Double Hydroxides

A series of Mg₂Al_<i>x</i>V_1–<i>x</i>–LDH (LDH = layered double hydroxide) was synthesized by using a facile method, and well-mixed derived oxides were obtained after calcinations. These catalysts were further tested for H₂S selective oxidation. Meanwhile, the physicochemical properties of the catalysts were investigated by various methods. It was observed that vanadium species existed mainly in the form of isolated V⁵⁺ in distorted [VO₄],Mg₃V₂O₈ and VO²⁺. Significantly, these catalysts exhibited high catalytic activities in a relatively lower range of reaction temperatures (100–200 °C) as a result of the well-dispersed vanadium species and excellent moderate basicity property. A catalytic reaction mechanism was proposed as follows: H₂S was first adsorbed on the Mg–O–Mg band of MgO (moderate basic sites), forming S^2– and H₂O, then the S^2– was oxidized to S_<i>n</i> by V⁵⁺, simultaneously, forming oxygen vacancies and V⁴⁺. Finally, V⁴⁺ was oxidized to V⁵⁺ by O₂, and O^2– was incorporated into oxygen vacancies. In addition, the catalyst deactivation was mainly due to the decrease in moderate basic sites. Moreover, the formed less-active VOSO₄ also contributed to the catalyst deactivation