DFT Reactivity Descriptors and Catalysis - Vrije Universiteit Brussel

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Results for the 4T cluster (1Al, 3Si) model • rate constants 300-800K E A • 2 mechanisms consecutive* vs direct E A 193 127 kJmol -1 * Pre-exponential factor is higher so that at higher T the two mechanisms become competing (400K) (effect of ∆S act ) Direct mechanism in line with experimental data ( no stable intermediates) <strong>and</strong> confirmed in periodic boundary calculations by Van Santen (J.Am.Chem.Soc.123, 2799(2001)) • Influence of substituents: the role of activation hardness (MHP at work) ∆ η = η −η Z. Zhou, R.G.Parr, J.Am.Chem.Soc, 112, 5720 (1991) react TS obtained via HOMO –LUMO gap E A (kJmol -1 ) k (400K) ∆η (activation hardness) Benzene 127.1 (4) 5.6 10 -24 0.0597 (4) Toluene o 114.2 (1) 3.6 10 -23 0.0493 (1) m 123.9 (3) 3.1 10 -24 0.0536 (3) p 117.8 (2) 2.2 10 -22 0.0499 (2) • electrondonating character of CH 3 -group shows up in E A . • E A <strong>and</strong> activation hardness match Pag. 30-9-2008 26
• Local level • Softness indicators fail Charge controlled reaction Cfr. Hardness of electrophilic species CH 3+ (η= 7.83V) • Dominance of electrostatic interactions η C(arom) |q c | (arom) derived from Electrostatic potential based ∆E cc ∼ q q ( ar ) c( methanol ) R cc Charges (CHELPG) for adsorbed reactants η c(ar) ∆E cc Benzene 0.0259 -9.85 Toluene o 0.1522 -67.63 m 0.0033 -1.36 p 0.0548 -20.19 Hardness related quantities are adequate reactivity descriptors for these reactions A.M.Vos, K.H.Nulens, F.De Proft, R.A. Schoonheydt, P.Geerlings, J.Phys.Chem.B, 106, 2026 (2002) Pag. 30-9-2008 27
Page 1 and 2: DFT Reactivity Descriptors and Cata
Page 3 and 4: Outline 1. Robert Schoonheydt and t
Page 5 and 6: Pag. 30-9-2008 5
Page 7 and 8: Pag. 30-9-2008 7
Page 9 and 10: Pag. 30-9-2008 9
Page 11 and 12: 2. Chemical Concepts from DFT Funda
Page 13 and 14: Conceptual DFT (R.G. Parr, W. Yang,
Page 15 and 16: Identification of two first derivat
Page 17 and 18: • Ambiguity in the definition var
Page 19 and 20: Applications until now mostly on (g
Page 21 and 22: 3. Some applications of global and
Page 23 and 24: The Two Step Consecutive Mechanism
Page 25: • Rate Constant Evaluation • Tr
Page 29 and 30: 3.2 Lewis acid Catalysis: the role
Page 31 and 32: Transition States C m H 3Cb X 1 H 2
Page 33 and 34: Cyclic TS characterized by several
Page 35 and 36: 4. Towards the Inclusion of Confine
Page 37 and 38: Atoms • previous work (1992-2005)
Page 39 and 40: An atom test case: helium Radial De
Page 41 and 42: Ethylene: planar confinement • Sa
Page 43 and 44: A first try: an order of magnitude
Page 45 and 46: Epilogue: looking back at the 1979-
Page 47: 6. Acknowledgments Prof. Wilfried M

DFT Reactivity Descriptors and Catalysis - Vrije Universiteit Brussel

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