Abstract
The topotactic transformation mechanism and memory effect of NiAl- and MgFe- layered double hydroxides (LDHs) are investigated by density functional theory (DFT)-based molecular simulation under their two key thermal decomposition temperatures (365, 800 °C for NiAl-LDHs, and 380, 800 °C for MgFe-LDHs). The results show that at the first temperature, the interlayer carbonate in both LDHs decompose to CO2 and H2O via a monodentate intermediate. During the dehydroxylation of the layers, for both LDHs the metal cations maintain their original distribution within the LDH (0 0 1) facet, while migrating substantially along the c-axis direction, and the layered structure of MgFe-LDHs is destroyed earlier than those of NiAl-LDH. Meanwhile, MgFe-LDHs can keep the memory effect longer than NiAl-LDHs, and the memory effect will disappear when the four-coordinated metal cations increased. At 800 °C, the layered structure of NiAl-LDHs is slightly destroyed, while a complete collapse of layered structure occurs in MgFe-LDHs. These results agree well with the experimental findings. This work will be helpful for the design and preparation of nanocatalysts derived from LDHs precursors.
Acknowledgements
We acknowledge the National Supercomputing Center in Shenzhen and the ‘Chemical Grid Project’ of Beijing University of Chemical Technology for providing the computational resources.