Effect of molybdenum on mercury oxidized by V2O5–MoO3/TiO2 catalysts

• Mo can obviously enhance Hg0 oxidized by V2O5–MoO3/TiO2 even only with O2 present.
• Hg0 oxidized by V2O5–MoO3/TiO2 follows Mars–Maessen mechanism.
• Mo showed no effect in Hg0 oxidized by pure MoO3/TiO2 catalyst.
• Mo6+ can assist to oxidize V3+ to V5+ for mercury oxidation.

A detail process of sol–gel method was introduced to prepare V2O5–MoO3/TiO2 catalyst powders containing different quantities of vanadium pentoxide and molybdenum trioxide in this study. Powder for the application in these SCR catalysts for mercury oxidation was tested in laboratory for the first time. The results indicated that titanium–vanadium–molybdenum catalysts are of higher mercury oxidation efficiency than titanium–vanadium catalysts. Especially the V2O5–MoO3/TiO2 catalyst contained 5 wt% vanadium pentoxide and 5 wt% molybdenum trioxide (TV5M5), even with only the present of 6% O2, it still performed a strong mercury oxidation ability. Elemental mercury oxidized by V2O5–MoO3/TiO2 catalysts was found to follow the Mars–Maessen mechanism. Molybdenum trioxide could not directly oxidize Hg0, but molybdenum in high valence could assist to oxidize vanadium in low valence to increase the number of lattice oxygen for mercury oxidation according to the X-ray photoelectron spectroscopy results. In addition, HCl exhibited a promotional effect on mercury oxidation across TV5M5, the concentration of oxidized mercury escaped from the catalyst surface increased as the content of HCl introduced into the 6% O2/N2 atmosphere increasing.