For all Ptn/alumina samples, both C2D4 and D2 desorption were observed, with size-dependent variations in the intensities and sub-structure of the desorption features. C2D4 desorption was bi-modal, with a ~200 K peak similar to that for Pt-free alumina but with higher intensity, and a stronger feature only seen with Ptn present, beginning near 230 K and going to completion by ~450 K. In the 2 nd and subsequent TPD runs, the ~200 K peak strengthened, while the higher temperature feature weakened rapidly.