SO2 promoted V2O5-MoO3/TiO2 catalyst for NH3-SCR of NOx at low temperatures.

Graphical abstract Highlights • Presence of SO 2 promotes NO x conversion of monolithic V 2 O 5 -MoO 3 /TiO 2 catalyst. • Lower SO 2 oxidation activity leads to fewer sulfates deposits on VMoTi-S. • High proportioned tridentate sulfates on VMoTi-S act as strong Brønsted acid sites. • More active polymeric vanadates form on the Mo-modified catalyst after sulfation. • Consequently facilitated NH 2 formation enhances SCR activity of VMoTi-S. Abstract V 2 O 5 -MoO 3 /TiO 2 and V 2 O 5 -WO 3 /TiO 2 monolithic catalysts were evaluated for selective catalytic reduction (SCR) of NO x with NH 3 in the presence of SO 2 and H 2 O. After a durability test at 220 °C for 30 h, the NO x conversion of V 2 O 5 -MoO 3 /TiO 2 increased from 70% to 88% while it decreased slightly over V 2 O 5 -WO 3 /TiO 2. The catalysts were characterized by H 2 temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of NH 3 , thermo-gravimetric (TG) analysis, temperature-programmed decomposition (TPD) of deposits, temperature-programmed surface reaction (TPSR) of ammonium bisulfates with NO, surface-enhanced Raman spectroscopy (SERS), ultraviolet-visible (UV–vis) and diffuse reflection infrared Fourier transform (DRIFT) spectroscopy. There were fewer sulfates deposits on VMoTi-S catalyst due to lower SO 2 oxidation which was related to less V O V bonds on the Mo-modified catalyst. The as-formed high proportioned stable tridentate sulfates on VMoTi-S catalyst acted as strong Brønsted acid sites, and more active polymeric vanadates remained on this catalyst to activate the absorbed NH 4 +. The separation of acid sites and active sites which facilitates NH 2 formation was suggested to be responsible for the promoted SCR activity of V 2 O 5 -MoO 3 /TiO 2 during NH 3 -SCR reaction. [ABSTRACT FROM AUTHOR]