A New Insight into Catalytic Ozonation with Nanosized Ce-Ti Oxides for NOx Removal: Confirmation of Ce-O-Ti for Active Sites

Amorphous cerium and titanium mixed oxides (Am-CeTi) and crystalline cerium and titanium mixed oxides (Ct-CeTi), prepared by coprecipitation and impregnation methods, respectively, were successfully utilized in catalytic ozonation for NOx removal. The catalytic activity has been confirmed to be determined by the concentration of center dot OH radicals. Am-CeTi shows higher activity than Ct-CeTi. Ce-O-Ti linkage bonds, with an interaction between Ce and Ti on an atomic scale, are confirmed for the first time to be an active site for catalytic ozonation to remove NOx. The incorporation of more Ce results in an amorphous structure (Am-CeTi) and a higher number of Ce-O-Ti linkage bonds as compared to that of Ct-CeTi, and the Ce-O-Ti structure is directly observed by HR-TEM. Moreover, such incorporation is responsible for less surface defects and lower densities of surface hydroxyl groups because of the elimination of crystalline defects. The higher catalytic activity of Am-CeTi indicates the small effect of surface defects and surface groups.