DFT‐Based Simulation and Experimental Validation of the Topotactic Transformation of MgAl Layered Double Hydroxides

Abstract

The thermal topotactic transformation mechanism of MgAl layered double hydroxides (LDHs) is investigated by a combined theoretical and experimental study. Thermogravimetric differential thermal analysis (TG-DTA) results reveal that the LDH phase undergoes four key endothermic events at 230, 330, 450, and 800 °C. DFT calculations show that the LDH decomposes into CO2 and residual O atoms via a monodentate intermediate at 330 °C. At 450 °C, the metal cations almost maintain their original distribution within the LDH(001) facet during the thermal dehydration process, but migrate substantially along the c-axis direction perpendicular to the (001) facet; this indicates that the metal arrangement/dispersion in the LDH matrix is maintained two-dimensionally. A complete collapse of the layered structure occurs at 800 °C, which results in a totally disordered cation distribution and many holes in the final product. The structures of the simulated intermediates are highly consistent with the observed in situ powder XRD data for the MgAl LDH sample calcined at the corresponding temperatures. Understanding the structural topotactic transformation process of LDHs would provide helpful information for the design and preparation of metal/metal oxides functional materials derived from LDH precursors.

The effects of (di‐,tri‐valent)‐cation partitioning and intercalant anion‐type on the solubility of hydrotalcites

“…Figure 1C shows the differential thermogravimetric mass loss (DTG) traces for hydrotalcite with Mg/Al = 2 over the temperature range 35°C‐975°C. It is seen that as expected, surface‐sorbed and interlayer water is released between 35°C and 250°C, 56,57 while the mass loss between 250°C and 550°C was assumed to be due to dehydration/dehydroxylation, decarbonation or desulfurization of the hydrotalcite phases, respectively 58‐60 . It must be noted, that without analysis of the evolved gas, the intercalant species cannot be identified unambiguously.…”

“…It is seen that as expected, surface-sorbed and interlayer water is released between 35°C and 250°C, 56,57 while the mass loss between 250°C and 550°C was assumed to be due to dehydration/dehydroxylation, decarbonation or desulfurization of the hydrotalcite phases, respectively. [58][59][60] It must be noted, that without analysis of the evolved gas, the intercalant species cannot be identified unambiguously. Therefore, the mass loss is assumed to be the result of the intercalant species of interest and not contaminants.…”

Interfacial Fe5C2-Cu catalysts toward low-pressure syngas conversion to long-chain alcohols

“…In this report, we used Cu–Fe–LDHs as a precursor. After a structural topological transformation followed by an activation treatment 30–34 , Fe 5 C 2 cluster supported on Cu particle catalyst is obtained. Fe 5 C 2 clusters (~2 nm) are highly dispersed over the surface of Cu nanoparticles (~25 nm) which creates rich interfacial sites; and the Cu 4 Fe 1 catalyst with optimized Fe 5 C 2 –Cu interface exhibits a CO conversion of 53.2% and space time yield of 0.101 g g cat −1 h −1 for long-chain alcohols, at a low operation pressure (1 MPa).…”

Acetate intercalated Mg–Al layered double hydroxides (LDHs) through modified amide hydrolysis: a new route to synthesize novel mixed metal oxides (MMOs) for CO2capture

“…In order to investigate the effect of the synthesis method and different starting precursors on and structural properties of these materials is an ongoing research. [50][51][52] The only crystalline phase observed in the resultant MMOs is MgO and the nature of the aluminium containing oxide/hydroxide is amorphous. MMOs from Mg-Al-acetate LDHs show (Fig.…”