That requires the macro in the PRO version. The X1 is the entry level model and doesn't have the shutdown macro. However, assuming you are at the PS3 menu level, it is a simple matter to add a shutdown macro in the Harmony itself. If you search on that on this forum you will find several discussions about doing just that.
Keep in mind though, since the X1 does not have a PS button function, it is more complicated to shut down if you are in a game or watching a movie since you have to return to the PS3 menu first.