Neutralization of Sodium Azide using Ammonium Cerium Nitrate
I think that you are doing fine!
The azide anion can be used for quite some amazing chemistry, but it's rather toxic and harmful for the environment.
Admittedly, I'm too lazy right now to look up the redox potentials or to write the reaction equation, but
CAN should be able to oxidize $\ce{N3-}$ all the way up to $\ce{NO3-}$, which is safe to be disposed.

Update
Judging from memory can result in bad advices!
A closer look at the SDS of both compounds shows that both have

H410 Very toxic to aquatic life with long lasting effects. and

P273 Avoid release to the environment.


Consequently, the combined solutions (with excess of CAN) should not be poured down the drain, but collected (aqueous inorganic waste).