The structure sensitivity of palladium particles for hydrodeoxygenation of propanoic acid is evaluated using Pd(100), Pd(211)1 and Pd(111)1 model surfaces. A combination of density functional theory calculations (with and without inclusion of dispersion interactions) and microkinetic modeling is used to investigate the activity of each surface. Adsorbate-adsorbate interactions are considered using the model of Grabow et al.2 The surface with the highest turnover frequency is Pd(100) and Pd(111) is the second most active surface. The dominant reaction pathways and most abundant surface species for Pd(100) are identified and compared with those of the less active surfaces. Our results show that all three surfaces prefer a decarbonylation mechanism over a decarboxylation mechanism. The predominant pathway over all palladium surfaces starts with a dehydrogenation at the α-carbon, followed by C-OH bond cleavage and decarbonylation. Finally, the effects of liquid water on the predominant pathways and turnover frequencies are discussed. Liquid phase effects are computed within our implicit solvation method for solid surfaces (iSMS).3 Overall, liquid water significantly facilitates the decarboxylation pathways such that decarbonylation and decarboxylation become competitive.4 Also, liquid water effects reduce the free site coverage and accelerates some elementary reactions such as the dehydrogenation of propionate which involves a product species that is strongly stabilized by polar solvents since the carboxylate group is now directed towards the solvent (the reactant species adsorbs through the carboxylate group). [1] S. Behtash, J. Lu, C. T. Williams, J. Monnier, A. Heyden, J. Phys. Chem. C. 119 (2015) 1928-1942. [2] L. C. Grabow, B. Hvolbæk and J. K. Nørskov, Top. Catal. 53 (2010) 298-310. [3] M. Faheem, S. Suthirakun, A. Heyden, J. Phys. Chem. C 116 (2012) 22458-22462. [4] S. Behtash, J. Lu, M. Faheem, A. Heyden. Green Chem. 16 (2014) 605-616.

Theoretical study of the reaction mechanism and structure sensitivity of the hydrodeoxygenation of propanoic acid over Pd catalysts in vapor and liquid phase environments

251st National Meeting (2016)

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