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

Abstract

A series of Mg 2 Al x V 1– x –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 2 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 5+ in distorted [VO 4 ],Mg 3 V 2 O 8 and VO 2+ . 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 2 S was first adsorbed on the Mg–O–Mg band of MgO (moderate basic sites), forming S 2– and H 2 O, then the S 2– was oxidized to S n by V 5+, simultaneously, forming oxygen vacancies and V 4+ . Finally, V 4+ was oxidized to V 5+ by O 2, 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 VOSO 4 also contributed to the catalyst deactivation.