MoO₃/TiO₂ catalyst with atomically dispersed O-Mo-O structures toward improving NH₄HSO₄ poisoning resistance for...

Slow progress in discovering new catalysts to circumvent the problem of ammonium bisulfate (NH₄HSO₄, ABS) poisoning has hindered further development of selective catalytic reduction (SCR) technology of NO_x with ammonia (from numerous industrial processes) in afterburning systems at temperatures below dew point of ABS (typically between 280 °C and 320 °C). Recently, we have explored the use of atomically dispersed Mo species on TiO₂ particles (hereafter denoted as MoO₃/TiO₂) as highly efficient catalyst for NH₃-SCR reaction. In the present study, it will be shown that this type of catalyst is highly resistant to ABS poisoning for NH₃-SCR reaction, overcoming a major issue afflicting the application of commercial V₂O₅-WO₃/TiO₂ catalyst at temperatures below the dew point of ABS. Aberration-corrected scanning transmission electron microscopy (STEM) suggests that most of the Mo species are present in atomically dispersed form in the MoO₃/TiO₂ catalyst. SO₂ oxidation measurements show that the MoO₃/TiO₂ catalyst exhibits a substantially lower SO₂ oxidation rate compared to the commercial V₂O₅-WO₃/TiO₂, mitigating ABS formation. Furthermore, decomposition of ABS on MoO₃/TiO₂ surface is found to be extremely facile. Temperature-programmed surface reaction (TPSR) with NO shows that the decomposition temperature of ABS over MoO₃/TiO₂ is 70 °C lower than that found on the commercial V₂O₅-WO₃/TiO₂ catalyst. Our investigations provide valuable information for the development of NH₃-SCR catalysts with exceptional resistance to ABS poisoning for NO_x emission control.