Dear friends,
I had prepared Pd NPs impregnated micro porous carbon based catalyst through green route. The XRD and HRTEM of the same shows the presence of both Pd(0) and Pd(+2) on it. Since the support material is micro porous, expecting Pd(0) to be present in the external surface of the support. However, the XPS of the catalyst shows peaks only for Pd(+2). What could be the reason for this? How can I correlate these two observations? Please help me. Thanks in advance.
ANSARI P
How large are your nanoparticles? Is it possible that it's a penetration depth issue? I suppose your TEM works with much higher electron kinetic energies so you may see signals from regions so deep that XPS doesn't see them.
Dear Mr. Jurgen, thanks for your response. My particles are of 7-10 nm in size. And my support is composed of mainly micro pores, i.e with diameter less than 2 nm. So, i am expecting the Pd(0) particles on the external surface of the support. In that case, XPS should give Pd(0) peaks, right? But, its not giving.... At the same time, XRD and HRTEM indicates the presence of both Pd(0) and Pd(+2). I stuck because of this anomalous behavior of XPS data.
Didi you record your spectra using an excitation energy of 1253.6 eV(Mg source)? In that case, using the curve for inorganic materials from this work:
Article Quantitative Electron Spectroscopy of Surfaces: A Standard D...
you get a penetration depth of
Dear Mr. Jurgen, the spectra were recorded using Al-K∞ radiation (1486.6 eV).
Well, that makes the penetration depth 3.2nm, but it doesn't fundamentally change too much.
My point was the following: the Pd(0) may be too deep inside so XPS does not see it which doesn't mean it's not there deeper down where an electron microscope with its higher penetration depth may get it.
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