Selective Catalytic Reduction of Nitric-oxide With Ammonia Using Moo3/tio2 - Catalyst Structure and Activity

A series of titania supported MoO3 catalysts (0-20 wt.-% MoO3) were prepared by dry impregnation. The influence of the MoO3 content on their catalytic performance for the selective catalytic reduction (SCR) of nitric oxide by ammonia in the presence of oxygen, as well as on their textural and structural properties has been studied. The samples were characterized by XRD, XPS, IR, and BET and porosimetry measurements. The coverage of the TiO2 support by surface polymeric molybdenum species (where molybdenum is octahedrally coordinated) increases with the molybdenum loading. The formation of a layer of these interacting species on top of the titania surface is complete in the range 15-20 wt.-% MoO3. The formation of crystallites of bulk MoO3 starts before the completion of this surface layer (at around 10 wt.-% MoO3) and increases progressively as the molybdenum loading increases from 10 to 20 wt.-% MoO3. The SCR activity of the MoO3/TiO2 catalysts increases as the MoO3 content increases to 15 wt.-% and then, for a further increase of the molybdenum loading, it slightly decreases. No specific influence of the molybdenum content on the resistance of catalysts towards SO2 was observed; the same slight deactivation took place, when the SCR activity was measured in the presence of SO2 in the feed, for all samples. Our results indicate that the octahedrally coordinated polymeric molybdenum surface species are mainly responsible for the exhibited SCR activity of the MoO3/TiO2 catalysts.