Selective Catalytic Oxidation of H<sub>2</sub>S over
Well-Mixed Oxides Derived from Mg<sub>2</sub>Al<sub><i>x</i></sub>V<sub>1–<i>x</i></sub> Layered Double Hydroxides
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Abstract
A series
of Mg<sub>2</sub>Al<sub><i>x</i></sub>V<sub>1–<i>x</i></sub>–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 H<sub>2</sub>S 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 V<sup>5+</sup> in distorted [VO<sub>4</sub>],Mg<sub>3</sub>V<sub>2</sub>O<sub>8</sub> and VO<sup>2+</sup>. 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: H<sub>2</sub>S was first adsorbed on the Mg–O–Mg
band of MgO (moderate basic sites), forming S<sup>2–</sup> and
H<sub>2</sub>O, then the S<sup>2–</sup> was oxidized to S<sub><i>n</i></sub> by V<sup>5+</sup>, simultaneously, forming
oxygen vacancies and V<sup>4+</sup>. Finally, V<sup>4+</sup> was oxidized
to V<sup>5+</sup> by O<sub>2</sub>, and O<sup>2–</sup> 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 VOSO<sub>4</sub> also contributed to the catalyst
deactivation