  While freestanding clean graphene is essential for various applications,
existing technologies for removing the polymer layer after transfer of graphene
to the desired substrate still leave significant contaminations behind. We
discovered a method for preparing ultra-clean freestanding graphene utilizing
the catalytic properties of platinum metals. Complete catalytic removal of
polymer residues requires annealing in air at a temperature between 175 and
350{\deg}C. Low-energy electron holography investigations prove that this
method results in ultra-clean freestanding graphene.
