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 NOx 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 NOx emission control.