A B3LYP Study on the C-H Activation in Propane by Neutral and +1 Charged Platinum Clusters With 2-6 Atoms

T. Cameron Shore, Drake Mith, Doug DePrekel, Staci McNall, and Yingbin Ge*Department of Chemistry, Central Washington University, Ellensburg, WA 98926

Method comparison against exp. data

Global optimization of Pt clusters (e.g. Pt5)

Ptn + C3H8 → Ptn---C3H8 → H−Ptn−CH(CH3)2

Notes and ReferencesThe following experimental data are used as the benchmark: the electron affinity (EA) of Pt and Pt2 are 205.0 kJ/mol and 183.1 kJ/mol, respectively; the ionization energy (IE) and bond energy (BE) of Pt2 are 864.4 kJ/mol and 303 kJ/mol, respectively; the bond energy of PtH is 332 kJ/mol; the ionization energies of PtC, PtO, and PtO2 are 912 ± 5 kJ/mol, 965 ± 10 kJ/mol, and 1095 ± 5 kJ/mol, respectively; the bond energies of PtC, PtO, and PtO2 are 574 ± 7 kJ/mol, 415 ± 12 kJ/mol, and 426 ± 13 kJ/mol, respectively; the equilibrium bond distances of Pt2, PtH, PtC, and PtO are 2.333 Å, 1.53 Å, 1.679 Å, and 1.727 Å, respectively.

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

T.C. Shore, D. Mith, DePrekel, S. McNall, Y. Ge SA (2013) A B3LYP study on the C—H activation in propane by neutral and +1 charged low-energy platinum clusters with 2-6 atoms: A B3LYP study, Reaction Kinetics, Mechanisms and Catalysis, in press, 2013

Potential energy surface (Pt5 + C3H8)

Global minima of Pt2-6

Global minima of +1 charged Pt2-6

Computational method• B3LYP density functional theory• 6-31G(d) on C and H• LanL2DZ (f) basis set and LanL2 effective core potential on Pt

Conclusions• Pt2 is less active than larger Pt3-6 clusters.• +1 charged Pt clusters are more active than neutral ones.• Electron pushing surface hinders the catalytic ability of the

supported Pt clusters; electron withdrawing surface is preferred.

Acknowledgements• CWU SEED Grant• CWU College of the Sciences Faculty Development Fund• CWU Department of Chemistry

Removal of a 2nd H produces propene

Pt10 and Pt10+ local minima + C3H8

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.

• Vajda et al. find Pt8-10 clusters are much more active than traditional catalysts towards propane in 4 steps1:

1. Ptn + C3H8 → H−Ptn−CH(CH3)2

2. H−Ptn−CH(CH3)2 → (H)2−Ptn−propene3. (H)2−Ptn−propene + ½ O2 → Ptn−propene + H2O + heat4. Ptn−propene + heat → Ptn+ propene

• We studied the Pt cluster size and charge effects regarding the rate limiting step 1. Global minimum

+

Propane (C3H8) Propene (C3H6)

local minimum

local minimum

Various Ptn structures

global minimum

Global minimum vs. Local minimum

Mean absolute errors of calculated electron affinity, ionization energy, & bond energy

Mean absolute errors of calculated bond distances

B3LYP B3PW91 PBE PW91 MP2

25 26 36 38 91

B3LYP B3W91 PBE PW91 MP2

0.010 0.003 0.011 0.010 0.037

local minimum E

δ

Electron withdrawing surface

e-

Ptn+ + C3H8 → Ptn

+---C3H8 → H−Ptn+ −CH(CH3)2