(361a) First Principles Investigation of SOx (x = 0 - 4) Chemistry On Pt (111) and Pd (111) | AIChE

(361a) First Principles Investigation of SOx (x = 0 - 4) Chemistry On Pt (111) and Pd (111)


Sharma, H. - Presenter, Lawrence Livermore National Laboratory
Sharma, V., Univesity of Connecticut
Mhadeshwar, A. B., University of Connecticut
Ramprasad, R., University of Connecticut

First principles investigation of
SOx (x = 0 - 4)
chemistry on Pt (111) and Pd (111)


Hom N. Sharma1, V. Sharma2,
Ashish B. Mhadeshwar1,3 and R. Ramprasad1, 2,*


1Department of Chemical and Biomolecular Engineering,
University of Connecticut, Storrs, CT

2Material Science and
Engineering, University of Connecticut, Storrs, CT

at ExxonMobil Research & Engineering, Annandale, NJ


Sulfur oxides
(SOx (x = 0 ─ 4)) in the diesel engine exhaust are one
of the major factors contributing toward deactivation of the noble metals
(Pt/Pd) based emissions aftertreatment catalysts [1, 2]. Interactions
of SOx with the catalyst metals and supports are associated with
changes in various structural, morphological, and electronic properties, which can
lead to sulfate formation [3, 4].  Despite many experimental
and computational studies, SOx interactions with metal surfaces and their
impact on catalytic activity are not clearly understood. In the present study,
we explore the SOx (x = 0 ─ 4) chemistry in terms of interactions
and oxidation pathways on Pt(111) and Pd(111) surfaces using first principles
density functional theory (DFT) [5]. We have
identified various stable configurations (figure 1), which reveal the charge
redistribution patterns, and molecular orbital interactions of SOx
on both surfaces during adsorption. The possible reaction pathways and
estimated activation barriers for SOx oxidation on the metal
surfaces ? identified using climbing image nudged elastic band (CI-NEB) method [6] ? are found to
be in good agreement with the experimental observations. This comprehensive and
comparative study provides important insights about SOx chemistry on
Pt and Pd surfaces, which can be useful to design and improve sulfur resistance
catalyst materials.

Figure 1: Representative stable configurations
of SOx molecules on Pt(111): (a) S (fcc) η1 Sf
, (b) SO (fcc) η1-Sf , (c) SO (fcc) η2
SbOa, (d) SO2 (fcc) η2 SbOa,
(e) SO2 (fcc) η3 SaOaOa,
(f) SO2 (bridge) η1 S┴, (g) SO3
(fcc) η3 OaOaOa, (h) SO3
(fcc) η3 SaOaOa, and (i) SO4
(fcc) η3 OaOaOa. The
number super-scripted to η represents the number of atoms in a molecule
coordinated to the metal surface; and the subscripts a, b, and f
represent the atop, bridge, and fcc hollow sites, respectively.


[1]   T. Kolli, M. Huuhtanen, A.
Hallikainen, K. Kallinen, R. Keiski, Catal. Lett. 127 (2009) 49-54.

[2]   A. Russell, W.S. Epling,
Catal. Rev. Sci. Eng. 53 (2011) 337-423.

[3]   J.A. Rodriguez, J. Hrbek, Acc.
Chem. Res. 32 (1999) 719-728.

[4]   H.N. Sharma, S.L. Suib, A.B.
Mhadeshwar, in: Novel Materials for Catalysis and Fuels Processing, ACS, 2013,
In press.

[5]   G. Kresse, J. Furthmüller,
Phys. Rev. B. 54 (1996) 11169.

[6]   G. Henkelman, B.P. Uberuaga,
H. Jonsson, J. Chem. Phys. 113 (2000) 9901-9904.