1. 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 98926 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 8:213-216 2.Xiao L, Wang LC (2007) Methane activation on Pt and Pt 4 : A density functional theory study. J Phys Chem B 111:1657-1663 3.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 13:6883-6890 4.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 2-6 + 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 -0.183, -0.208, and -0.224 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