Instead of a certificate, it could be a simple email from the director's side to all concerned.
In my opinion, it will look more appropriate and worthwhile if the director calls the respective team, thanking them for their contribution and great help. It's a good gesture from the director that he wants to highlight their good deed. But it is not something employees will preserve; these certificates can show or produce to someone, so I suggest a verbal thanksgiving will be much more effective as it will facilitate direct interaction with the director.