MoO3/TiO2 catalyst with atomically dispersed O-Mo-O structures toward improving NH4HSO4 poisoning resistance for selective catalytic reduction of nitrogen oxides

Abstract

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.