Structure and Energetics of (111) Surface of γ-Al2O3: Insights from DFT Including Periodic Boundary Approach

Abstract

The (111) surface of γ-alumina has been reexamined, and a new (111) surface model has been suggested. The local structure of this new surface of γ-alumina, (111)n, has been optimized by the density functionals along with the full electron basis sets by using periodic boundary condition. This newly modeled (111)n surface is characterized by the same stability as that of the (110) surface, and its surface energy amounts to 2.561 J/m2, only about 0.002 J/m2 larger than that of (110). Three different types of the tricoordinated Al centers have been identified on (111)n. Molecular orbital (MO) analysis and the population analysis demonstrate that one type of Al, Al(I), is a nonpaired electron center. The singly occupied MO on Al(I) center is expected to play an important role in the catalytic activities of the γ-alumina. Moreover, the neighboring Al (Al(III)) on the (111)n surface provides suitable acceptance position for the electron donating groups. The defected surfaces of (111)n are found to be having a similar stability. The detachment of Al(I) from the (111)n surface results in disappearance of the nonpaired electron centers. Meanwhile, the attachment of Al(I) on (111)n surface will produce rich nonpaired electron centers on this new surface. Therefore, this newly defined surface is expected to attract the research interests in the catalytic activities of γ-alumina.