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First-Principles Assessment of the Reactions of Boric Acid on NiO(001) and ZrO2(1̅11) Surfaces

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journal contribution
posted on 10.05.2012, 00:00 by Priyank V. Kumar, Michael P. Short, Sidney Yip, Bilge Yildiz, Jeffrey C. Grossman
The present study investigates the adsorption and dissociation reaction pathways of boric acid, B­(OH)3, and the reaction kinetic descriptors on NiO(001) and ZrO2(1̅11) surfaces. Density functional theory is employed for ground-state calculations, while the nudged elastic band method is used for obtaining reaction barriers. Strong electron correlations in the case of NiO are included using the DFT + U approach. Adsorption of boric acid on clean ZrO2(1̅11) is found to be more favorable compared with that on NiO(001), in agreement with prior experiments. Dissociative adsorption is observed to dominate over molecular adsorption in the case of ZrO2(1̅11), whereas NiO(001) favors molecular adsorption. The most stable configuration for B­(OH)3 on NiO(001) is a hydrogen-bonded molecular structure, Nis-(OH)­B­(OH)­(OH)···Os (s = surface atom), with an adsorption energy of −0.74 eV. On ZrO2(1̅11), a single O–H dissociated structure, Zrs-(O)­B­(OH)­(HO)-Zrs + Os-H, with an adsorption energy of −1.61 eV, is the most stable. Our results reveal lower activation barriers for B­(OH)3 dissociation on NiO(001) than on ZrO2(1̅11). We demonstrate the importance of both the surface transition-metal atom and oxygen states and discuss bonding mechanisms leading to different adsorption configurations on such metal oxides. The analysis of surface reactivity presented here is useful in designing metal oxides for catalytic applications and is of significant importance in fuel materials durability in nuclear energy systems.