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Issue 16, 2014
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The roles of surface structure, oxygen defects, and hydration in the adsorption of CO2 on low-index ZnGa2O4 surfaces: a first-principles investigation

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Abstract

The effects of the surface atomic and electronic structures, oxygen defects, and hydration on CO2 adsorption on ZnGa2O4(100), (110), and (111) surfaces were studied using density functional theory (DFT) slab calculations. For the perfect (100) surface, the most stable adsorption state involved the Zn–O–Ga bridge site, with an adsorption energy of 0.16 eV. In the case of the (110) and (111) surfaces, the strongest binding occurred on the Zn–O bridge sites, with much lower adsorption energies of −0.22 eV and −0.35 eV, respectively. In addition, the perfect surfaces showed CO2 activation ability, but dissociation adsorption could not proceed. The oxygen vacancies on these three surfaces (1) made the metal sites beside them carry less positive charge and further reduced the adsorption energies on these metal sites, and (2) created efficient adsorption sites that allowed even dissociative adsorption. The most favorable molecular and dissociative adsorption states both involved the O3c vacancy site of the (100) surface, and these two processes were spontaneous with adsorption energies of 0.74 eV and 0.80 eV, respectively. When H2O molecules are present on the perfect and defective surfaces, the generation of hydrogen bonds between H2O and CO2 would slightly enhance the stability of adsorption (except for that on the (111)-Vo3c surface), making them energetically favorable. However, the co-adsorption of H2O could also increase the energy barriers for the decomposition reactions on the defective surfaces, making them kinetically unfavorable. Furthermore, the oxygen vacancy defects showed good activity for H2O adsorption and decomposition, as well. Thus, when both H2O and CO2 were present in the adsorption system, H2O would compete with CO2 for the oxygen vacancy sites and further decrease the amount of CO2 adsorption and decomposition. These findings have important implications for the decomposition of CO2 on the ZnGa2O4 surfaces and can provide theoretical guidance for chemists to efficiently synthesize ZnGa2O4 catalysts.

Graphical abstract: The roles of surface structure, oxygen defects, and hydration in the adsorption of CO2 on low-index ZnGa2O4 surfaces: a first-principles investigation

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Publication details

The article was received on 02 Jan 2014, accepted on 22 Feb 2014 and first published on 25 Feb 2014


Article type: Paper
DOI: 10.1039/C4CP00004H
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Citation: Phys. Chem. Chem. Phys., 2014,16, 7538-7547
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    The roles of surface structure, oxygen defects, and hydration in the adsorption of CO2 on low-index ZnGa2O4 surfaces: a first-principles investigation

    C. Jia, W. Fan, X. Cheng, X. Zhao, H. Sun, P. Li and N. Lin, Phys. Chem. Chem. Phys., 2014, 16, 7538
    DOI: 10.1039/C4CP00004H

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