A series of Ce0.90Co0.10O2 - (delta) and Ce-0.90 (-) xCuxCo0.10O2 - (delta) (x = 0.03, 0.07 and 0.10) catalysts synthesized by an alkaline hydrothermal method were utilized as ozonation catalysts for the NOx (x = 1, 2) removal at low temperatures. A novel catalyst -duct separation apparatus for denitrification by catalytic ozonation was developed by our group. Ce0.83Cu0.07Co0.10O2 - (delta) exhibits the highest catalytic activity (91.5% removal at 120 degrees C), whereas Ce0.83Cu0.07Co0.10O2 - (delta) presents the lowest (74.1% removal at 120 degrees C). Only NO3- is detected in the tail solutions. The catalytic performance presents a positive relationship with the corresponding center dot OH concentration. center dot OH radical can be "transferred" from catalyst surface to the duct, prolonging activation time through its own reproduction reaction. The surface -OH activation, not the surface -OH density determines the " OH concentration in the present method. Ce0.83Cu0.07Co0.10O2 - (delta) contains a large number of high -activation bridging -OH, whereas the bridging -OH is absent in Ce0.83Cu0.07Co0.10O2 - (delta). Therefore, Ce0.83Cu0.07Co0.10O2 - (delta) shows much higher activation for promoting the formation of center dot OH than Ce0.83Cu0.07Co0.10O2 - (delta).