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B3LYP study of the dehydrogenation of propane catalyzed by Pt clusters: Size and charge effects T. Cameron Shore, Drake Mith, Staci McNall, and Yingbin.

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Presentation on theme: "B3LYP study of the dehydrogenation of propane catalyzed by Pt clusters: Size and charge effects T. Cameron Shore, Drake Mith, Staci McNall, and Yingbin."— Presentation transcript:

1 B3LYP study of the dehydrogenation of propane catalyzed by Pt clusters: Size and charge effects T. Cameron Shore, Drake Mith, Staci McNall, and Yingbin Ge* Department of Chemistry, Central Washington University, Ellensburg, WA Method comparison against exp. data Global optimization of Pt clusters (e.g. Pt 5 ) Pt n + C 3 H 8 → Pt n ---C 3 H 8 → H−Pt n −CH(CH 3 ) 2 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 (2004) Structures of platinum clusters: Planar or spherical? J Phys Chem A 108: ; 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 Potential energy surface (Pt 5 + C 3 H 8 ) Global minima of Pt 2-6 Global minima of +1 charged Pt 2-6 Percent errors of the calculated bond energy (BE), ionization energy (IE), and electron affinity (EA) using various computational methods with the LANL2DZ (f) basis set and ECP on Pt and 6-31G(d) basis set on C & O. Computational method B3LYP density functional theory 6-31G(d) on C and H atoms LanL2DZ (f) basis set and LanL2 effective core potential (ECP) on Pt Transition states are verified by minimum energy path calculations Conclusions The energy barrier for the Pt n + C 3 H 8 → H−Pt n −CH(CH 3 ) 2 reaction decreases as the size of the neutral Pt n cluster increases from 2 to 6, and then it starts to level off. +1 charged Pt clusters are significantly more active than their neutral counterparts. Pt 4 + is the least active among all studied +1 charged Pt n clusters; this finding agrees with Adlhart et al. experiments. 3 We conjecture that, in heterogeneous catalysis, electron- pushing metal oxide surfaces may hinder the electron transfer from propane to Pt n and thereby lower the catalytic ability of the surface-supported Pt n clusters. Acknowledgements CWU SEED Grant CWU College of the Sciences Faculty Development Fund CWU Department of Chemistry Removal of a 2nd H produces propene Pt 10 and Pt 10 + local minima + C 3 H 8 Introduction Each label consists of point group, relative energy in kJ/mol, and # of imaginary frequencies if applicable. Energy includes electronic energy and zero-point vibrational energy. Relative energies are in kJ/mol. M stands for multiplicity. The quintet PES is the lowest energy reaction path for Pt 5. Vajda et al. find Pt 8-10 clusters are much more active than traditional catalysts towards propane in 4 steps 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 studied the Pt cluster size and charge effects regarding step 1. Neutral Pt n +1 charged Pt n Global minimum


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