Adsorption of guaiacol on Fe (110) and Pd (111) from first principlesby Alyssa J.R. Hensley, Yong Wang, Jean-Sabin McEwen

Surface Science

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P1Q2 (1 2Q3 en 3 tate 4 , US 5 A 6 7 8 9 10 11 12 13 14 15 16 van der Waals corrections 17rfac 18bed 19dso 20catalysts. Here, we study the adsorption of guaiacol on Fe (110) and Pd (111) using dispersion-corrected density 21s as both of thesemetals are of interest as hydrodeoxygenation catalysts for the con22 23 24 25 26 27 28 29 30 31 32 33 345 36 7 38 39 ications 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67atics is weakened on 68el Fe and Pd surfaces 69the Pd/Fe system [10,

Surface Science xxx (2015) xxx–xxx

SUSC-20683; No of Pages 9 October 29, 2015; Model: Gulliver 5

Contents lists available at ScienceDirect

Surface S .eUgreat importance to the design and optimization of catalysts by theSomorjai research group [5–9].

Of particular interest to our group is elucidating the inter- and intrawork has shown that the adsorption of arom model Pd/Fe surfaces as compared to both mod due to the change in Pd's electronic structure inN

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Oproduce surfaces with superior performance as compared to monometallic surfaces. However, to better optimize and design these bimetallic surfaces, a detailed knowledge of the inter- and intra-surface interactions is necessary for both the bimetallic surface and its monometallic constituents. The application of surface science techniques to gain insight into the bimetallic and monometallic structure and electronic states during various chemical processes has been shown to be of doping Fe catalysts with small amounts of precious metals (e.g. Pd or

Pt), and such catalysts have shown a high activity for the HDO of phenols, such as guaiacol and m-cresol, producing aromatic hydrocarbon products with a high selectivity [10,11].

While these Fe-based bimetallic catalysts look promising as HDO catalysts, knowledge of the complex inter- and intra-surface interactions which lead to the high catalytic activity is lacking. Our previoussurface interactions for Fe-based bimetallic c

Fe-based bimetallic catalysts has shown tha high activity for the hydrodeoxygenation (HD ⁎ Corresponding author at: Department of Chemistry

Pullman, WA 99164, USA. Tel.: +1 509 335 8580; fax: +

E-mail address: js.mcewen@wsu.edu (J.-S. McEwen). http://dx.doi.org/10.1016/j.susc.2015.10.030 0039-6028/© 2015 Published by Elsevier B.V.

Please cite this article as: A.J.R. Hensley, et aRas catalysts, from petroischer–Tropsch catalysts nable properties which to be highly selective for the HDO of phenols [10,11], it is known to easily form oxides and carbides, quickly deactivating under reaction conditions [14]. However, this surface deactivation can be avoided byleum refining [1] to catalytic converters [2] to F [3] to methanol fuel cells [4], due to their tuBimetallic surfaces have many appl1. Introduction R

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Daromatic ring) adsorption configurations were examined and the resulting adsorption and molecular distortionenergies showed that the vertical sites were only physisorbed while the horizontal sites were chemisorbed on both metal surfaces. A comparison of guaiacol's horizontal adsorption on Fe (110) and Pd (111) showed that guaiacol had a stronger adsorption on Pd (111) while the Fe (110) surface distorted the C\\O bonds to a greater degree. Electronic analyses on thehorizontal systems showed that the greater adsorption strength for guaiacol on

Pd (111) was likely due to the greater charge transfer between the aromatic ring and the surface Pd atoms.

Additionally, the greater distortion of the C\\O bonds in adsorbed guaiacol on Fe (110) is likely due to the greater degree of interaction between the oxygen and surface Fe atoms. Overall, our results show that the Fe (110) surface has a greater degree of interaction with the functional groups and the Pd (111) surface has a greater degree of interaction with the aromatic ring. © 2015 Published by Elsevier B.V. (e.g. phenolics and furanics) [10–13], a key step in transforming pyrolysis bio-oils into more useable biofuel. While Fe alone has been shownFe (110)

Pd (111) v ersion of bio-oils to useable biofuels. Both vertical (via the oxygen functional groups) and horizontal (via theGuaiacol adsorption functional theory calculationAdsorption of guaiacol on Fe (110) and Pd

Alyssa J.R. Hensley a, Yong Wang a,b, Jean-Sabin McEw a The Gene & Linda Voiland School of Chemical Engineering and Bioengineering, Washington S b Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352 c Department of Physics and Astronomy, Washington State University, Pullman, WA 99164, US d Department of Chemistry, Washington State University, Pullman, WA 99164, USA a b s t r a c ta r t i c l e i n f o

Available online xxxx

Keywords:

Density functional theory

The catalytic properties of su electronic structure of adsor level understanding of the a j ourna l homepage: wwwatalysts. Recent work on t these catalysts have a

O) of bio-oil oxygenates , Washington State University, 1 509 335 4806. l., Surf. Sci. (2015), http://dx.dR

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F 11) from first principles a,c,d,⁎

University, Pullman, WA 99164, USA

A es are highly dependent upon the effect said surfaces have on the geometric and reactants, products, and intermediates. It is therefore crucial to have a surfacerption of the key species in a reaction in order to design active and selective cience l sev ie r .com/ locate /susc7015]. Further examination of the adsorption andHDOmechanismof phe71nol on monometallic Fe (110) and Pd (111) surfaces showed that the 72high HDO activity of the Fe catalysts and ring saturation activity of Pd 73catalysts is likely due to the stronger charge transfer between the 74oxygen functional group and surface Fe and the aromatic ring and 75surface Pd [16,17]. These results strongly suggest that Fe is the active 76site for the HDO of phenolics on Pd/Fe surfaces. As for the role of Pd in oi.org/10.1016/j.susc.2015.10.030

T77 these bimetallic catalysts, several studies on the reducibility of Fe2O3 78 doped with Pd and the stability of the Pd/Fe surface under steam 79 exposed has shown that the Pd dopant likely maintains the high HDO 80 activity of the Fe surface by protecting said surface from deactivation 81 via oxidation [11,18]. This work connects to that of the Somorjai re82 search group as they showed that doping Fe single-crystal surfaces 83 with potassium and aluminumoxide enhances the activity of Fe for am84 monia synthesis by decreasing the adsorption energy of ammonia and 85 maintaining an active Fe surface structure under reaction conditions 86 [19,20], together suggesting that the relatively abundant metal Fe can 87 be easily functionalized to produce highly active catalysts. 88 While our previous work has elucidated many of the inter- and 89 intra-surface interactions in the Fe-based bimetallic catalysts that 90 contribute to the high HDO activity of said catalysts, much is still un91 known in this area. In this study,we examine the effect of complex func92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 12529] exchange-correlation functional to account for van der Waals cor126rections which has shown to strongly affect the adsorption energies of 127both physisorbed and chemisorbed species [30,31]. When using the 128optB88-vdW, we switched to the Perdew, Burke, and Ernzerhof (PBE) 129[32,33] functional to generate the PAW core potentials as we found 130that the adsorption energy results for the optB88-vdW functional with 131the PW91 generation of the PAW core potentials varied significantly 132with minor changes to the model's vacuum thickness. All other param133eters were identical to those used in our previous work studying the 134adsorption of phenol on Fe (110) and Pd (111) [16]. In the density of 135states analyses, the energy levels were normalized such that the Fermi 136level was set to zero. For gas phase guaiacol, the Fermi level was taken 137to be halfway between the HOMO and LUMO states, similar to the 138work of Mittendorfer et al [34]. 139All of the studied adsorption configurations of phenol on the 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 157 158 159 160 161 162 163 165 166 167 xyg 2 A.J.R. Hensley et al. / Surface Science xxx (2015) xxx–xxxU