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 NO x removal. The catalytic activity has been confirmed to be determined by the concentration of ·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 NO x . 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.