Alkali-Free Hydrothermally Reconstructed NiAl Layered Double Hydroxides for Catalytic Transesterification

Abstract

NiAl layered double hydroxides (LDHs) are promising bifunctional catalysts comprising tunable redox and Lewis acidic sites. However, most studies of NiAl LDH employ alkali hydroxide carbonate precipitants which may contaminate the final LDH catalyst and leach into reaction media. Here, we report an alkali-free route to prepare NixAl LDHs with a composition range x = 1.7 to 4.1 using (NH4)2CO3 and NH4OH as precipitants. Activation of LDHs by calcination–rehydration protocols reveal NixAl LDHs can be reconstructed under mild hydrothermal treatment (110 °C for 12 h), with the degree of reconstruction increasing with Ni content. Catalyst activity for tributyrin transesterification with methanol was found to increase with Ni content and corresponding base site loadings; TOFs also increased, suggesting that base sites in the reconstructed LDH are more effective for transesterification. Hydrothermally reconstructed Ni4.1Al LDH was active for the transesterification of C4–C12 triglycerides with methanol and was stable towards leaching during transesterification.

Hydrogen-Free Deoxygenation of Oleic Acid and Industrial Vegetable Oil Waste on CuNiAl Catalysts for Biofuel Production

“…In all samples, patterns of crystalline materials with reflections characteristic of LDHtype compounds were identified. The four intense and well-defined peaks present at angles 2θ < 30 • correspond to the basal distances of the planes (003), (006), (009) and (0012) [54,55]. Further, the two wider and less intense peaks at higher angles (2θ > 30 • ) are also characteristic of LDHs, corresponding to (012) and (110) reflections [54,55].…”

“…The four intense and well-defined peaks present at angles 2θ < 30 • correspond to the basal distances of the planes (003), (006), (009) and (0012) [54,55]. Further, the two wider and less intense peaks at higher angles (2θ > 30 • ) are also characteristic of LDHs, corresponding to (012) and (110) reflections [54,55]. It is important to note that the presence of segregated copper or aluminum phases was not found in the diffractograms of the CuNiAl LDHs, which demonstrates that the method used, with a theoretical Cu/Ni ratio ≤ 0.4, was effective in obtaining LDH-type compounds containing Cu.…”

Catalytic pyrolysis of biomass to produce bio‐oil using layered double hydroxides (LDH)‐derived materials

“…In general, not all the LDO can be constructed back LDH material because of different chemical composition or structure of LDO than LDH, stability/reactivity of LDO, lack of suitable interlayer space. Reconstructed LDH are actively utilized as catalytic materials for various chemical reactions (Prakruthi et al., 2015; Tajuddin et al., 2022). The reconstructed LDH possess some disadvantages such as poor cycling performance, less surface area and defected structure and metal oxide loading (Ye et al., 2022) that hinders their catalytic activities.…”

Review on the contribution of ultrasounds in layered double hydroxides synthesis and in their performances

“…This effect is defined as the reconstruction of a mixed oxide obtained by thermal decomposition of LDHs immersed in an aqueous solution [77]. Generally, the reconstruction of LDHs is performed by hydrothermal treatment [78]. Álvarez et al [42] studied the reconstruction of Zn-Al and Zn-Al-Mg LDH by mechanical stirring and ultrasonication during rehydration.…”