Nanoparticle palladium hydride

The coadsorption of CO and hydrogen on Al203-supported palladium nanoparticles was found to be quite different from that on the single crystal. As shown in the preceding section on palladium hydride formation (Section IV.C.4), H subsur-face/bulk dissolution occurs more easily in palladium nanoparticles. Consequently, preadsorbed H can be replaced from the palladium particle surface even at 100 K, leading to a CO-saturated surface (cf. Fig. 31c) thus, in contrast to the observations... 

Pd(l 1 1) discussed above, the explosive desorption of the hydride phase through a CO-layer which occurs only for palladium nanoparticles is remarkable. 

To explain the different behavior for nanoparticles, it is important to realize that for palladium not only absorption in the bulk of the material is important, but also the sorption of hydrogen near the surface should be considered. It is known that palladium forms surface hydrides, with about 1 H per Pd surface atom. However, sorption in subsurface sites is also important, as evidenced by studies on (flat (110) surfaces [45]. Figure 10.9 shows a schematical representation of the energy levels for the hydrogen atom at the surface, in subsurface sites, and absorbed in the bulk. 

Rose, A., Maniguet, S., Mathew, R.J. et al. (2003) Hydride phase formation in carhon supported palladium nanoparticle electrodes investigated using in situ EXAFS and XRD. Physical Chemistry Chemical Physics, 5, 3220-3225. 

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