Palladium ions (e.g., $\ce{Pd^2+}$) can be reduced to $\ce{Pd}$ by more reactive metals such as zinc. Metal oxides such as $\ce{ZnO}$ are very stable but can its atoms in the oxide structure still be displaced by Pd? I know the answer is probably "No" but in one of my samples $\ce{ZnO}$ nanoparticles were removed from the solution after I added $\ce{Pd^2+}$ solution to the system and $\ce{Pd}$ nanoparticles were formed. The solvent was methanol. After washing the solution and drying I did XPS and no trace of zinc was observed but saw $\ce{Pd}$ peaks.
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$\begingroup$ The metals aren’t connected to the Swedish entrepreneur Alfred Nobel but to the English adjective to nobility: noble. As for the actual question, I sadly cannot give you an answer. $\endgroup$ – Jan Dec 16 '18 at 17:02
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$\begingroup$ Did you measure the size of the nano-particles? According to Wikipedia, at most, the XPS instrument will only probe $\pu{20 nm}$ into a sample. Thus, I wonder, $\ce{Pd}$ has been deposited on $\ce{ZnO}$ surface. "Palladium Deposition on $\ce{Pt}$ Surface by Reduction of $\ce{Pd^2+}$ Ions with Organic Substances" has been studied before (link.springer.com/article/10.1023/A:1010314807520). $\endgroup$ – Mathew Mahindaratne Dec 16 '18 at 22:44
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Zinc chemistry is overwhelmingly that of the +2 oxidation state, it does not go higher. For ZnO to reduce Pd+2, the Zn has to go up from +2 which it cannot. If you are getting reduction of Pd+2, Zn is not responsible.
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$\begingroup$ Perhaps ZnO is catalyzing the reduction of Pd(II) to Pd(0) with methanol as the reducing agent (oxidized to formaldehyde). I presume the Pd(II) is stable in methanol. $\endgroup$ – user55119 Dec 16 '18 at 23:43
