MoO/TiO catalyst with atomically dispersed O-Mo-O structures toward improving NHHSO poisoning resistance for selective catalytic reduction of nitrogen oxides.

Slow progress in discovering new catalysts to circumvent the problem of ammonium bisulfate (NHHSO, ABS) poisoning has hindered further development of selective catalytic reduction (SCR) technology of NO 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 TiO particles (hereafter denoted as MoO/TiO) as highly efficient catalyst for NH-SCR reaction. In the present study, it will be shown that this type of catalyst is highly resistant to ABS poisoning for NH-SCR reaction, overcoming a major issue afflicting the application of commercial VO-WO/TiO 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 MoO/TiO catalyst. SO oxidation measurements show that the MoO/TiO catalyst exhibits a substantially lower SO oxidation rate compared to the commercial VO-WO/TiO, mitigating ABS formation. Furthermore, decomposition of ABS on MoO/TiO surface is found to be extremely facile. Temperature-programmed surface reaction (TPSR) with NO shows that the decomposition temperature of ABS over MoO/TiO is 70 °C lower than that found on the commercial VO-WO/TiO catalyst. Our investigations provide valuable information for the development of NH-SCR catalysts with exceptional resistance to ABS poisoning for NO emission control.