Figs. and show diminishing amounts of D2 desorption/carbon deposition over the TPD sequence, and in our previously reported C2D4 TPD study of Pt4/alumina and Pt4Ge/alumina, we carried out 21-run TPD sequences to see if carbon deposition stopped at some level. The D2 desorption signal continued to decrease over the 21 runs, eventually dropping below the small m/z=4 mass spectrometer background, implying that carbon deposition asymptotically approaches some limiting value. For the Ptn clusters, this value exceeds one C atom/Pt atom, but for the PtnGem clusters, coking appears to self-limit at a relatively small value, of roughly two C atoms/cluster, approximately independent of cluster size.