SELECTIVE CATALYTIC REDUCTION OF NITRIC-OXIDE WITH AMMONIA USING MOO3TIO2 - CATALYST STRUCTURE AND ACTIVITY/

A series of titania supported MoO3 catalysts (0-20 wt.-% MoO3) were pr epared 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 speci es (where molybdenum is octahedrally coordinated) increases with the m olybdenum loading. The formation of a layer of these interacting speci es 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 com pletion 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 MoO 3 content increases to 15 wt.-% and then, for a further increase of th e 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 activi ty was measured in the presence of SO2 in the feed, for all samples. O ur results indicate that the octahedrally coordinated polymeric molybd enum surface species are mainly responsible for the exhibited SCR acti vity of the MoO3/TiO2 catalysts.