B3LYP study on the lowest energy Pt clusters and their reactivity towards small alkanes T. Cameron Shore, Drake Mith, and Yingbin Ge* Department of Chemistry, Central Washington University, Ellensburg, WA Method comparison References 1.Vajda S, Pellin MJ, Greeley JP, Marshall CL, Curtiss LA, Ballentine GA, Elam JW, Catillon-Mucherie S, Redfern PC, Mehmood F, Zapol P (2009) Subnanometre platinum clusters as highly active and selective catalysts for the oxidative dehydrogenation of propane. Nat Mater 8: Xiao L, Wang LC (2007) Methane activation on Pt and Pt 4 : A density functional theory study. J Phys Chem B 111: Adlhart C, Uggerud E (2007) Mechanisms for the dehydrogenation of alkanes on platinum: Insights gained from the reactivity of gaseous cluster cations, Pt n +, n=1-21. Chemistry-a European Journal 13: Ge YB, Shore TC, Mith D, McNall SA (2012) Activation of a central C−H bond in propane by neutral and +1 charged platinum clusters: A B3LYP study, submitted to Journal of Theoretical and Computational Chemistry Global minima of Pt 2-6 and Pt Percent errors of the calculated bond energy (BE), ionization energy (IE), and electron affinity (EA) using the various computational methods with the LANL2DZ (f) basis set on Pt and 6-31G(d) on main group elements. The studied species include Pt, Pt 2, PtC, PtO, PtO 2. Computational method B3LYP density functional theory 6-31G(d) on C and H atoms LANL2DZ(f) basis set and effective core potential on Pt Possible low-energy structures were studied exhaustively. Neutral clusters and corresponding potential energy surfaces were calculated with a multiplicity of 1,3,5,7; the +1 charged ones with a multiplicity of 2,4,6,8. Conclusions The Pt n + R-H → H-Pt n -R reaction involves electron density transfer from alkane to Pt n. Reactivity: C 3 H 8 > C 2 H 6 > CH 4. This is because -CH 3 pushes electrons. E.g., the Mulliken charge on Pt 2 is , , and in the Pt 2 ---RH reactant complex, where R=CH 3, C 2 H 5, and C 3 H 7, respectively. Larger Pt n clusters better disperse the negative charge and hence have lower energy barrier and more negative reaction energy. Positively charged Pt n + clusters are generally more active than their neutral counterparts. Pt 4 + is the least active among all Pt n + clusters; this finding agrees with experiments. 4 Acknowledgements CWU SEED Grant CWU College of the Sciences Faculty Development Fund CWU Department of Chemistry Introduction Vajda et al. found Pt 8-10 clusters are much more active than tradition catalysts towards propane in a 4-step mechanism. 1 1.Pt n + C 3 H 8 → H−Pt n −CH(CH 3 ) 2 2.H−Pt n −CH(CH 3 ) 2 → (H) 2 −Pt n −propene 3.(H) 2 −Pt n −propene + ½ O 2 → Pt n −propene + H 2 O + heat 4.Pt n −propene + heat → Pt n + propene We focus on neutral and +1 charged Pt n + H−R → H−Pt n −R, where R = -CH 3, -C 2 H 5, and -CH(CH 3 ) 2, to study the size and charge effects. Potential energy surfaces of Pt n + RH → H-Pt n -R & Pt n + + RH → H-Pt n -R + Potential energy surfaces of Pt n + RH → H-Pt n -R & Pt n + + RH → H-Pt n -R + Pt n + RH → H-Pt n -R Pt n + + RH → H-Pt n -R + Relative energy of the reactant complex vs. the Mulliken charge on the Pt atoms in the Pt n ---C 3 H 8 reactant complex. Apparent energy barrier vs. relative energy of reactant complex for the Pt n + C 3 H 8 → Pt n ---C 3 H 8 → H-Pt n -C 3 H 7 reaction. Pt n + C 3 H 8 endothermic