Jahn-Teller Effect And The Stability Of Cu-Containing Layered Double Hydroxides

Layered double hydroxides (LDHs), also known as hydrotalcite-like compounds or anionic clays, which has a special strcture and properties; copper is commonly used for the catalytic active component, therefore Cu-Containing Layered Double Hydroxides and its derivatives are widely used in a variety of catalytic reactions. In this paper, we used density functional theory to study the microstructure properties of Cu-Containing Layered Double Hydroxides.Jahn-Teller effect of the Cu-Mg-Al layered double hydroxides:We proposed a periodic interaction model for the layered double hydroxides, CuxMg3-xAl-LDHs (x=0-3). Based on density functional theory, the geometry of CuxMg3-x Al-LDHs was optimized using the CASTEP program. Jahn-Teller effect and the stability were investigated by analyzing the geometric parameters, electronic arrangement, hydrogen-bonding, charge populations, and binding energies. The results showed that Jahn-Teller effect not only existed in the d orbital that was not filled of the Cu2+, but also existed in the p orbital that was not filled of Mg2+, and the two orbitals affected the Jahn-Teller distortion of the metal ion. In the CuxMg33-xAl-LDHs (x=0-3), both the octahedral of aluminum and magnesium existed in the stabilized octahedral form. Then with the increase of Cu2+in the layer, the octahedral of copper changed from the flattened one to the stable elongated one, and the Jahn-Teller stabilization energy of the system gradually increased. In general, with the increase of Cu2+in the layer, the distortion caused by Jahn-Teller effect made the strength of hydrogen-bonding and electrostatic interactions between the host layer and the guest weaker, the absolute value of the binding energy decreased, then the chemical stability of the system become worse, and this helped us from the theory to understand the Jahn-Teller effect better on the synthesis of copper-containing LDHs.Effect of divalent metal ions on the stability of Cu-containing layered double hydroxides:We proposed a periodic interaction model for the CuM2Al-Layered double hydroxides, M represented the different divalent metal ions that partially replaced copper ion. Based on density functional theory, the geometry of CuM2Al-LDHs was optimized using the CASTEP program. The stabilities of Cu-containing layered double hydroxides were investigated by analyzing the geometric parameters, electronic distribution, charge populations, hydrogen-bonding, and binding energies. The results showed that the electrostatic interactions between the host layer and the guest played a major role in the laminate thickness of the CUM2Al-LDHS; M ions had minor effect on the central Al3+and maj or effect on the Cu2+moreover, M ions with uniform distribution of valence electron had less impact. In addition, in the CuM2Al-LDHs, for which M ion’s valence electrons are uniform, both the electrostatic interactions between the host layer and the guest and hydrogen-bonding increase. In general, with the increase of the M ion’s period number, the distortion angle of the system increases, and the absolute value of the binding energy and the chemical stability of the system decrease. The stability of CuCo2Al-LDHs is the worst, because Co2+valence electrons are nonuniform distribution. This result contributes to comprehend the rule for the synthesis of Cu-containing LDHs.Theoretical investigation on the effect of trivalent metal Ions to structural properties and stability of Cu-containing layered double hydroxides:We propose a periodic interaction model for the layered double hydroxides, Mg4Cu2M2(OH)16(NO3-)2,(M=A13+, Ga3+, Cr3+, Fe3+, Co3+). Based on density functional theory, the geometry of Mg4Cu2M2(OH)16(NO3-)2was optimized using the CASTEP program. The stability was investigated by analyzing the geometric parameters, electronic arrangement, charge populations, hydrogen-bonding, and binding energies. In the CuMg2M-LDHs, the hydrogen-bonding plays a major role in the laminate thickness, as Al3+is progressively replaced by M3+during the formation of new-LDHs, the crystalline of LDHs is better. The electrostatic interactions between the host layer and the guest in the CuMg2M-LDHs where M is in the main group (Al and Ga) are stronger than where M is in the sub-group (Cr, Fe and Co). There are complex network of hydrogen bonds, which includes O-H…O and O-H…N, the hydrogen bonding strength and the calculated binding energies of the CuMg2M-LDHs including both the main group cations (Al3+, Ga3+) and the sub-group cations (Cr3+, Fe3+and Co3+) decreased with the increasing of the period or group number, the host and the guest are away from each other. In general, the chemical stability of the CuMg2M-LDHs where M is in the main group is stronger than where M is in the sub-group. Therefore, this work provides a detailed understanding of how the electronic structure of different trivalent cations, bond lengths, cell angles and the Mulliken population of the cluster play a significant role in the structural properties and relative stability of the corresponding LDHs.