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Abstract
A memory effect is the ability to restore the original, lamellar layered double hydroxide structure. Herein, we have described 1) the changes in the structural and basic properties of ZnAl mixed oxides during their transformation into ZnAl-reconstructed LDHs (RE-LDHs); 2) the extraordinary properties of ZnAl RE-LDHs compared to the original ZnAl LDHs; and 3) the changes of basic properties during the interaction of ZnAl RE-LDHs with atmospheric CO2. Aldol condensation was selected as probe reaction to prove the catalytic potential of ZnAl RE-LDHs. We have described a target method for preparing ZnAl RE-LDHs with a large number of basic sites. ZnAl RE-LDHs possess significantly higher furfural conversion in the aldol condensation of furfural than MOs. The structural, textural, and basic properties of the studied materials were described by temperature-programmed analysis, X-ray diffraction, N2 adsorption, temperature-programmed desorption of CO2, and in-situ diffuse reflectance spectroscopy.
Highlights
Layered double hydroxides (LDHs) are the members of a group of layered materials comprising divalent (Mg, Zn, Ni, Cu, and Co) or trivalent (Al, Ga, and Fe) metal cations
The details are shown in the X-ray diffraction (XRD) patterns of the corresponding ZnAl LDHs (Supplementary Figure S1, Supplementary Table S1) and ZnAl mixed oxides of the corresponding materials (Supplementary Figure S1, Supplementary Table S2) or our previous studies on ZnAl mixed oxides (Smolakova et al, 2018; Dubnová et al, 2021)
The only exception is that ZnAl-1.9U-REH possesses a “shift of the edge of the band” value above its observed linear dependence on the content of the well-crystalline ZnO for ZnAl-X-REH. This can be explained by the low contribution of the amorphous ZnO phase and/or the high degree of the interaction of the ZnO and LDH phases, resulting in the detection of a low content of the XRD-detectable ZnO phase in ZnAl-1.9U-REH than in ZnAl-X-REH
Summary
Layered double hydroxides (LDHs) are the members of a group of layered materials comprising divalent (Mg, Zn, Ni, Cu, and Co) or trivalent (Al, Ga, and Fe) metal cations. A net positive charge in an LDH crystal lattice is compensated by extra-framework charge-balancing anions, generally carbonates (Bukhtiyarova, 2019). A distinctive feature of LDHs is their supposed memory effect. ZnM LDHs (M Al3+, Fe3+, Ga3+, and Ti3+) (Palmer et al, 2011; Wang and Zhang, 2012; Kikhtyanin et al, 2018; Bukhtiyarova, 2019; Santamaría et al, 2020; Szabados et al, 2020) can be prepared by several methods from various precursors of given metals, such as nitrates (Bellezza et al, 2014; Zeng et al, 2017; Tang et al, 2019), chlorides (Ambrogi et al, 2012; Zhang and Li, 2014) or sulfates (Mishra et al, 2017)
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