Is platinum present in a combustion chamber?
To elaborate on mins comment: platinum right now is selling for around \$1000 / troy ounce, which is ~\$14,500 / pound.  Nickel is selling for around \$4 / pound and cobalt is \$25/pound. Nickel and cobalt super alloys have sufficient temperature capability for jet engine applications.  So the choice is clear. Platinum is not mentioned because it is not used.