Figure 1. CO hydrogenation and chain propagation to

oxygenates as feedstock for lubricants, plasticizers,

and detergent

Methodology and Computational Setup

Background

Models Used

Effects of Cobalt Doping on OH/TiO2(110)

Oxygen Vacancy Formation Energy for

TiO2(110)

Acknowledgments Financial support was provided by the National Science Foundation under contract No. CBET1438227.

Support was also provided in part by institutional funds made available to JSM by The Gene and Linda Voiland

School of Chemical Engineering and Bioengineering at Washington State University.

We would also like to thank Mr. Gregory Collinge, Mr. Renqin Zhang, Ms. Alyssa Hensley, Ms. Fanglin Che, and

Ms. Emily Anderst, for helpful comments, discussion, and the welcome constructive critiques.

Cobalt Dopant Effects on Oxygen Vacancy Formations in TiO2(110)

Adam Saleh 1, Greg Collinge 1, Jean-Sabin McEwen1*

1. Washington State University, Pullman, Washington 99164 *Corresponding author: js.mcewen@wsu.edu

Structural Optimization Calculations

o VASP code[6,7]

o Exchange-correlation (xc) functionals: GGA-PW91[8]

o PAW + planewave basis[9]

o Planewave kinetic cutoff energy of 500 eV

o Gaussian smearing of 0.2 eV

o Monkhorst-Pack k-point grid of 6 6 1

o ISMEAR=−5: tetrahedron

o Definition of vacancy formation energy (Evf): Figure 2. 3D picture of p(2x1)

OH/TiO2(110) model expanded twice in

the x- and y- directions

CO hydrogenation to higher alcohols over CoCu-based heterogeneous catalysts an alternative to energy-intensive process of olefin hydroformylation [1-3]

Higher alcohols used as chemical feedstock

for plastics and other highly desirable

products. Producing them from renewable CO

and H2 would be a significant step toward

carbon-neutral energy independence

Experimental evidence suggests that the presence of oxides plays a critical role in the selectivity and activity of CoCu-based catalysts [1]

A catalytically relevant characteristic of oxides is their redox potential, which correlates to the energy of oxygen vacancy formation.

A C B

Figure 3. Models A and B show a top and a side view of the O/TiO2(110) and OH/TiO2(110) respectively. Model C shows the

top and side view of an example ¼ ML Co-doped hydroxyl terminated titania surface.

Operp Obridge Ohollow

Surface - 1.59 2.78

interstitial 2.86 2.40 2.50

Operp Obridge Ohollow

Surface -----

Interstitial

Operp Obridge Ohollow

Surface - 1.49 2.48

interstitial 2.80 2.80 2.42

Table 1. Energy (eV) Formation vacancy of

OH/TiO2(110)

Table 2. Energy (eV) Formation vacancy of

O/TiO2(110)

Figure 4. Locations of the oxygen vacancies of the

OH/TiO2(110)

Ti1 Ti2 O3 Ti3

Obridge 5.66 4.83 3.57

Ohollow 0 0.00

Obridge (farthest from Co)

5.43 - 3.05 -

Ohollow

(farthest from Co) - -

Ti1

Ti2

O3

Ti3

Obridge

Ohollow

Obridge (farthest from Co)

------ ------

Ohollow

(farthest from Co)

------

------

Table 3. Relative energy for oxygen vacancies with Co adsorbed on OH/TiO2(110). [--] are non-existent positions

Effects of Cobalt Doping on O/TiO2(110)

Ti1 O1 Ti2 O3 Ti3

Obridge 2.04 1.50 1.00 0.10 0.14

Ohollow 0.11 2.67 0.33

Obridge (farthest) 1.00 - - 0 -

Ohollow(farthest) - - 1.84 - 0.26

Ti1

O1

Ti2

O3

Ti3

Obridge

Ohollow

Obridge (farthest from Co)

------

------

------

Ohollow (farthest from Co)

------

------

------

Table 4. relative energy (eV) for oxygen vacancies with Co adsorbed on

O/TiO2(110)

Figure 7. Models of the oxygen vacancies with the different Co adsorption sites on

O/TiO2(110)

References

[1] Y. Xiang, R. Barbosa, N. Kruse, ACS Catal. 4 2014 2792-2800.

[2] Y. Xiang, R. Barbosa, X. Li, N. Kruse, ACS Catal. 5 2015 2929-2934.

[3] Y. Xiang, V. Chitry, P. Felfer, J. Cairney, S. Ringer, N. Kruse, J. Am. Chem. Soc. 135 2013 7114-7117.

[4] S. Julien, N. Kruse, ACS 134.39 2012 16135-16138.

[5] T. Pabisiak, A. Kiejna. Sol. State Comm. 144.7 2007 324-328.

[6] Buker, D. B., Todic, B., Ma, W., Jacobs, G., Davis, B. H., J. Catalysis, 2014, 228, 32-39

[7] Gnanamani, M. K., Catlysis Today, 2013, 25, 12-17

[8] Hibbitts, D. D., Loveless, B. T., Neurock, M., Iglesia, E., Angewandte Chemie intern‘l Ed. 2013, 52, 12273-12278

[9] Nilekar, A. U., Ruban, A. V., Mavrikakis, M. Surface Science, 2009, 603, 91-96 Liddicoat, P.

As cobalt (Co) is the most active metal for chain-lengthening in CoCu [4], discovering its effect on

the formation of oxygen vacancies in TiO2 is of high interest.

It has been shown that surface oxygen vacancy formation is much more facile than bulk oxygen

formation energy [5]

• Both oxygen and hydroxyl terminated surfaces are included since pH

conditions during catalyst preparation leads to the formation of hydroxyl

terminated surfaces, we include this system to account for the possibility of

such a system to exist under reaction conditions.

OH/TiO2(110)+1/2H2 → TiO2 + H2O

O/TiO2(110)+H2 → TiO2 + H2O

Ohollow

Obirdge

Obridge

(farthest from Co)

Ohollow

(farthest from Co)

Ohollow, I Obridge, I

OPerpendicular Obridge, S

Ohollow, S

Figure 6. Models of the oxygen vacancies with the different Co adsorption sites on O/TiO2(110)

• Ohollow removal with Co replacement is the most favorable Co/OH/TiO2(110)

O vacancy arrangement

Ohollow, Ti Ohollow Ti Optimized

Obridge (farthest from Co) Obridge (farthest from Co) optimized

• Obridge, removal with Co in the O3 hollow

site is the most favorable Co/O/TiO2(110)

O vacancy arrangement

Conclusion

O-vac

Layer

O-vac

Layer

O-vacancy

Starting Co ads site

Starting Co ads site

O-vac

Layer

Operp Obridge Ohollow

Surface -----

Interstitial

Figure 5. Locations of the oxygen vacancies of the

O/TiO2(110)

O-vac

Layer

O-vacancy

O-vacancy

Starting Co ads site

Starting Co ads site

• Oxygen energy vacancy of

O/TiO2(110) is an

agreements with Pabisiak et

al. OH/TiO2(110) follows the

same trend.

• Ohollow removal with Co

replacement is the most

favorable Co/OH/TiO2(110)

O vacancy arrangement

• Obridge, removal with Co in

the O3 hollow site is the most

favorable Co/O/TiO2(110)

O vacancy arrangement

O-vacancy