Selective Catalytic Oxidation of H2S over Well-Mixed Oxides Derived from Mg2AlxV1-x Layered Double Hydroxides

A series of Mg2AlxV1-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 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 degrees 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 S2- and H2O, then the S2- was oxidized to S-n by V5+, simultaneously, forming oxygen vacancies and V4+. Finally, V4+ was oxidized to V5+ by O-2, and O2- 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.