4th EucheMs chemistry congress

wednesday, 29-Aug 2012
s824
chem. Listy 106, s587–s1425 (2012)
Physical, theoretical and Computational Chemistry
Computational Chemistry – iii
o - 4 0 2
BridGeS Between the PhySiCS And CheMiStry
of MoLeCuLAr ConduCtorS
e. CAnAdeLL 1
1 ICMAB (CSIC), Laboratory of Electronic Structure of
Materials, Bellaterra, Spain
Molecular conductors are low-dimensional materials at the
crossroads of chemistry and physics. They offer fertile ground
where new ideas from the two disciplines can be brought together
to induce new phenomena or test new concepts. To have some
control over their properties it is advisable to understand their
electronic structure which provides the simplest link between the
chemical nature and the physical properties. These solids are
usually build from two different sublattices put together to induce
conducting properties in one of them.
Although simple tight-binding approaches have been
extremely successful in understanding many aspects of the
electronic structure of these solids, some features require a more
precise evaluation for a comparison with experimental results to
be meaningful. Accurate first-principles density-functional theory
(DFT) calculations are now possible for systems with large and
complex unit cells like many molecular conductors. However, to
fully exploit this potential, chemically oriented ways to analyze
the results are needed. In this presentation we will report the
results of DFT calculations using localized basis sets, which are
very well suited for this goal, for several of these solids.
Systems to be discussed include alpha-type BEDT-TTF
conductors and Bechgaard salts. Despite the fact that these salts
have been intensely studied for longtime some quite fundamental
aspects of their physical behavior are still not well understood. In
particular, we will discuss the origin of the low-temperature
modulation exhibited by alpha-(BEDT-TTF) KHg(SCN) and the
2 4
charge-ordering transition in alpha-(BEDT-TTF) I both of which
2 3
are associated with anomalies in their electrical conductivity. The
interaction of the conducting properties of one of the two
sublattices with other properties of the remaining sublattice will
also be considered.
Keywords: Electronic Structure; Conducting Materials;
Density Functional Calculations; Materials Science; Electronic
Transport;
Computational Chemistry – iV
4 th EucheMs chemistry congress
o - 4 0 3
tuninG CAtALytiC reACtivity on MetAL And
oxide SurfACeS: inSiGhtS froM dft
P. SAutet 1
1 University of Lyon and CNRS, Ecole Normale Supérieure de
Lyon Laboratoire de Chimie, Lyon, France
Tuning catalytic reactivity by atomic scale modifications of
the catalyst’s surface is a key aspect of fundamental catalysis. In
this lecture we will present and compare insights obtained from
DFT calculations on metal and oxide surfaces.
The first example will deal with the modification of Pt by
alloying. Mixing with Sn forms a PtSn surface alloy, decreasing
the reactivity of the Pt atoms, especially with C and H atoms. This
weakening has a direct influence on the selectivity for the
hydrogenation of unsaturated aldehydes by lowering the
adsorption energy of unsaturated alcohol, and allowing its
desorption from the catalyst. [1] In the case of butadiene selective
hydrogenation, the lower Pt-C interaction opens a new
hydrogenation pathway, where the C = C bond to be hydrogenated
in not coordinated to the surface. [2] This strongly reduces the
barrier for the selective pathways towards butene formation. [3]
The second example will deal with the influence of
coadsorbates on the surface, and we will focus on H O and OH
2
groups. On alumina, water can have a beneficial effect by
increasing the basicity of surface O atoms, hence favouring the
surface reactivity for methane or H dissociation. 2 [4] On a Rh or Pt
surface, OH groups form strong hydrogen bonds with alcohol
reactants, rendering OH activation easier, but disfavouring
C-H bond breaking [5, 6]
references:
1. D. Loffreda et al., Angewandte Chemie International
Edition, 48, 4978 (2009)
2. F. Delbecq, D. Loffreda, P. Sautet, J. Phys. Chem. Lett.,
1, 323-326 (2010)
3. F. Vigné, J. Haubrich, D. Loffreda, P. Sautet, F. Delbecq,
J. Catal. 275, 129 (2010)
4. R. Wischert et al., Angewandte Chemie International
Edition, 50, 3202-3205 (2011)
5. F. Auneau et al., Chem. Eur. J. 17, 14288-14299 (2011)
6. C. Michel, F. Auneau, F. Delbecq, P. Sautet, ACS catalysis,
1, 1430 (2011)
Keywords: heterogeneous catalysis; surface chemistry;
reaction pathways; Density Functional Theory;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc