Adsorption and Protonation of CO2 on Partially Hydroxylated γ-Al2O3 Surfaces: A Density Functional Theory Study

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• 作者：Yunxiang Pan ; Chang-jun Liu ; Qingfeng Ge
• 刊名：Langmuir
• 出版年：2008
• 出版时间：November 4, 2008
• 年：2008
• 卷：24
• 期：21
• 页码：12410-12419
• 全文大小：435K
• 年卷期：v.24,no.21(November 4, 2008)
• ISSN：1520-5827

文摘

Adsorption and protonation of CO₂ on the (110) and (100) surfaces of γ-Al₂O₃ have been studied using density functional theory slab calculations. On the dry (110) and (100) surfaces, the O−Al bridge sites were found to be energetically favorable for CO₂ adsorption. The adsorbed CO₂ was bound in a bidentate configuration across the O−Al bridge sites, forming a carbonate species. The strongest binding with an adsorption energy of 0.80 eV occurs at the O_3c−Al_5c bridge site of the (100) surface. Dissociation of water across the O−Al bridge sites resulted in partially hydroxylated surfaces, and the dissociation is energetically favorable on both surfaces. Water dissociation on the (110) surface has a barrier of 0.42 eV, but the same process on the (100) surface has no barrier with respect to the isolated water molecule. On the partially hydroxylated γ-Al₂O₃ surfaces, a bicarbonate species was formed by protonating the carbonate species with the protons from neighboring hydroxyl groups. The energy difference between the bicarbonate species and the coadsorbed bidentate carbonate species and hydroxyls is only 0.04 eV on the (110) surface, but the difference reaches 0.97 eV on the (100) surface. The activation barrier for forming the bicarbonate species on the (100) surface, 0.42 eV, is also lower than that on the (110) surface (0.53 eV).