Reactions of Methyl Radicals with Pd° Nanoparticles in Aqueous Solutions

Ronen Bar-Ziv, Chemistry, Ben-Gurion Univ. and Nuclear Research Centre Negev (N.R.C.N), Beer-Sheva, Israel
Israel Zilbermann, Chemistry, Ben-Gurion Univ. and Nuclear Research Centre Negev (N.R.C.N), Beer-Sheva, Israel
Guy Yardeni, Chemistry, Ben-Gurion Univ. and Nuclear Research Centre Negev (N.R.C.N), Beer-Sheva, Israel
Tomer Zidki, Biological Chemistry , Ariel University Center of Samaria, Ariel, Israel
Dan Meyerstein, Biological Chemistry , Ariel University Center of Samaria and Ben-Gurion Univ., Jerusalem, Israel

Alkyl radicals are important intermediates in electro-catalytic and heterogeneous catalytic processes. Nevertheless only few studies concerning the kinetics and mechanisms of reaction of alkyl radicals with M°-NPs suspended in solvents are available. All the reactions of M°-NPs and semi-conductor NPs suspended in aqueous solutions are very fast [1, 2]:

NPs + nR∙ → (NPs)-Rn    k > 1x108 M-1s-1

The mechanism of decomposition of the (NPs)-Rn transients thus formed depends on the nature of ·R and the NP. For R = ∙CH3 and NP = Ag°; Au°; TiO2; CuO the transients decompose via:

(NPs)-(CH3)n → (NPs)-(CH3)n-2 + C2H6

For Cu°-NPs the transients decompose via:

(Cu°-NPs)-(CH3)n + H+ → (Cu°-NPs)+-(CH3)n-1 + CH4

On the other hand (Pt°-NPs)-(CH3)n is stable in aqueous solution though traces of C2H6; C2H4 and CH4  are formed when methyl radicals react with Pt°-NPs.

As a consequence of the results obtained in the presence of Pt°-NPs, it was decided to investigate the reactions of methyl radicals with Pd°-NPs a metal with similar chemical properties. Indeed, the results obtained show that there are similarities between the two; however the yield of methane and ethane is considerably larger in the presence of Pd°-NPs and the number of methyls remaining bound to the Pd°-NPs is considerably smaller than for the Pt°-NPs.

In addition, the surface coverage causes a change in the electron density on the NPs causing a gradual change in the UV-Vis spectrum.


References

1.  R. Bar-Ziv, I. Zilbermann, O. Oster, G. Yardeni, H. Cohen, D. Meyerstein, Chemistry-a European Journal,  2012, 18, 4699-4805.

2.  R. Bar-Ziv, I. Zilbermann, T. Zidki, G. Yardeni , V. Shevchenko, D. Meyerstein,  Chemistry-a European Journal2012, 18, 6733-6736.


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