Sulfur content in crude oil is a harmful component in crude oil by-products and the environment. An accurate description of molecule–surface interactions is the first step toward a fundamental understanding of reactions on surfaces. Hydrodesulfurization (HDS) reaction is used for enhanced oil refining techniques as environmental regulations become more demanding. MoS2 surface selectivity absorption of dibenzothiophene (DBT) by using a catalytic compound is not fully understood. Usage of layered MoS2 promoted with Co as a catalytic agent for sulfur removal in crude oil processing has occurred successfully in the past 20 years. The design and study of structure/function is a must when indicating selective absorption of DBT components. Here we support earlier studies [fig 1.] on the promoted catalytic slab that have tried to answer the following questions : Where and how does the dissociation of H2 occur? Which surface structures form after the adsorption of hydrogen? How do they act when sulfur-containing molecules approach the surface?

1. Figure 1. Previous study including computational theory used to determine characterization and the
nature of the selective catalytic surface[1].
Introduction
• Sulfur content in crude oil is a harmful component in crude oil by-products and the
environment.
•An accurate description of molecule–surface interactions is the first step toward a
fundamental understanding of reactions on surfaces.[3]
•Hydrodesulfurization (HDS) reaction is used for enhanced oil refining techniques as
environmental regulations become more demanding.
• MoS2 surface selectivity absorption of dibenzothiophene (DBT) by using a catalytic
compound is not fully understood.
• Usage of layered MoS2 promoted with Co as a catalytic agent for sulfur removal in
crude oil processing has occurred successfully in the past 20 years.
•The design and study of structure/function is a must when indicating selective
absorption of DBT components.
• Here we support earlier studies [fig 1.] on the promoted catalytic slab that have tried
to answer the following questions :
•Where and how does the dissociation of H2 occur?
• Which surface structures form after the adsorption of hydrogen?
•How do they act when sulfur-containing molecules approach
the surface?[2]
Transition States of Selective HDS Reaction in MoS2/Co9S8 Molecular Interface:
First Principles
Svetlana Gelpi^1, Alvaro Laham2,Brenda Torres3, Gilles Berhault5, Russell R. Chianelli3 and Manuel Ramos* 4,5
1)Escuela de Ciencias y Tecnología, Universidad Metropolitana, San Juan, 00928, P.R.
2)AGMUS-Institute of Mathematics, Universidad Metropolitana, San Juan, 00928, P.R
3) Materials Research and Technology Institute, UT-El Paso, El Paso, TX. 79968
4) Physics Department, Universidad Autónoma de Cd. Juárez, MX. 32310
5) IRCELYON, CNRS – University of Lyon, Villeurbanne, 69100, France.
Experimental Methods
• Optimized interface for bulk MoS2/Co8S9 was used on all the experiments
[Ramos et al.].
• Optimized DBT molecule was used as the absorbent molecule.
• Quantum transitions kinetics were calculated using DMol3 code.
• Plane wave basis set was used during all the calculations with a Generalized
Gradient Approximation and Energy cutoff value: 5.5 Å. All species were treated
as Effective Core Potentials (ECP) with a real space cutoff of 3.7Å for Mo, 3.4Å
for Co, 3.3Å for S and 3.0Å for C and H atoms along with a basis set of double-
numerical functions (DN).
• Coordination location of reactant-product for selective Hydrodesulphurization
was set to two specific values in bulk MoS2/Co8S9, S-Co-Mo coordinated and S-
Mo-S.
• Adsorption energies describing interactions between the adsorbent and adsorbate
obey the following equation:
EKS = EBulk+DBT− (EBulk + EDBT)
Where Ebulk+DBT, EBulk and EDBT represent the total energy in MoS2/Co8S9
interface DBT molecule respectively.
Discussion and Results
• Linear synchronous transit maximum performed energy minimizations and
locate the activation energy along the minimum energy path (MEP).
• Reaction kinetics of H2 attachment into MoS2/Co9S8 bulk catalyst occurred in
6 steps [fig 2 and fig 3]:
• Attachment of H2 molecule three active termination sites ( Co, S and Mo).
• H2 molecule provokes a S-C breaking in DBT.
• DBT attaches to coordinated termination site in bulk catalyst.
• Interpolation of S and H atoms. S and termination site and H-C bonding.
• Attachment of H2 molecule to S atom to release of H2S gas.
•Dissociation reactions are highly structure-sensitive. The stepped, edged, or
open surfaces are generally much more active than the close-packed flat
surface.
•We determined unique features of metal surface reactions, for instance, the
early (late) TS of surface association(dissociation) reactions; the bonding
competition effect; and the surface structure sensitivity.[3]
Acknowledgements
•Universidad Metropolitana
•Materials Research and
Technology Institute, UT-El Paso
•National Science Foundation
• IRCELYON, CNRS – University
of Lyon
•Universidad Metropolitana.
•2012 Nanomaterial Summer
Research Program
Conclusion
• Transitional States using Quantum Computer analysis, serves as
fundamental basis during the understanding of synergic contact
between MoS2 and Co9S8 crystallographic structures.
• To locate the existence of endothermic and exothermic transitions
during the attachment of DBT molecules onto Mo, S and Co sites
are of high importance.
•Models help prove that promotion (addition of Co, Ni) provokes
the electronic configuration of electron donor acceptor relationships
between Co and Mo species, allowing the design of new catalytic
materials with better structure/function relationships.
References
• [1] Manuel Ramos , Gilles Berhault , Domingo A. Ferrer , Brenda Torres and Russell R.
Chianelli ‘’HRTEM and molecular modeling of the MoS2–Co9S8 interface: understanding the
promotion effect in bulk HDS catalysts”, Catal. Sci. Technol., 2012, 2, 164–178
•[2] Teodora Todorova, Valentin Alexiev and Thomas Weber, BULLETIN OF SCIENCE,
TECHNOLOGY & SOCIETY , 26(4),314-322,2006 , “DFT calculations of the dissociation of
H2 on (100) 2H-MoS2 surfaces: a key step in the hydroprocessing of crude oil”
[3] Zhi-Pan Liu,” Chemical reactions at surfaces and interfaces
from first principles: Theory and application” Pure Appl. Chem., Vol. 76, No. 12, pp. 2069–
2083, 2004.
Figure 3. (A) TEM image of a highly stacked slab presenting some curving effects and
interacting with the Co9S8 substrate. (B) HRTEM image of another region on which MoS2 is
spread onto a Co9S8 substrate. (C) Modeling of a Co9S8 (111) plane (D) Simulated TEM
picture of the Co9S8 (111) model shown in (C) showing the same honeycomb-like
arrangement than found experimentally in (B). (E) Schematic representation of the procedure
used to build the model interface between a cleaved (111) Co9S8 moiety and the (010)edge
plane of MoS2[1].
E.
Figure 2. Energies that resulted from DMol3 quantum code calculations proving that the
Sulfur edge interaction is endothermic are presented in the table above.
0
19.481
0
450.704
0
-459.672
0
366.554
0
50.465
-429.635
1 2 3 4 5 6 7 8 9 10 11
Transition State Activation Energies
Energy(kcal/mol) Progress of Reaction
2.Endothermic:
Absorption of
Sulfur from
DBT
1.Exothermic:
Absorption of
H2 into edge
3.Exothermic:
Dissociation
of Sulfur to
form H2S
Author of Correspondence: manuel.ramos@uacj.mx, maramos1@utep.edu
Chianelli et al. Rim-Edge Model
•Berhault and Chianelli proposed a
“Synergistic Contact Model” to describe
the nucleation and Catalytic activity for
MoS2 and Co9S8 [1].
•Chianelli and Daage proposed
the “Rim-Edge Model”[1]. 1. 2.
3.