The amount of norbornane obtained vs. the amount of Fe is plotted in Fig. 9. The slope of the straight line fitting the experimental points is 0.46, indicating that there is about 1 H per total atoms of Fe. Assuming that our nanoparticles are monodispersed with an average diameter of 2.7 nm as measured by TEM, we can approximate the amount of H2 per atom of Fe on the surface to 2.45 or about 5 H per 2 atoms of Fe. To account for this odd number, one can assume the presence of a bridging H2.