Synthesis of Chalcone Using LDH/Graphene Nanocatalysts of Different Compositions

Abstract

Layered double hydroxides (LDH) or their derived mixed oxides present marked acid-base properties useful in catalysis, but they are generally agglomerated, inducing weak accessibility to the active sites. In the search for improving dispersion and accessibility of the active sites and for controlling the hydrophilic/hydrophobic balance in the catalysts, nanocomposite materials appear among the most attractive. In this study, a series of nanocomposites composed of LDH and reduced graphene oxide (rGO), were successfully obtained by direct coprecipitation and investigated as base catalysts for the Claisen–Schmidt condensation reaction between acetophenone and benzaldehyde. After activation, the LDH-rGO nanocomposites exhibited improved catalytic properties compared to bare LDH. Moreover, they reveal great versatility to tune the selectivity through their composition and the nature or the absence of solvent. This is due to the enhanced basicity of the nanocomposites as the LDH content increases which is assigned to the higher dispersion of the nanoplatelets in comparison to bulk LDH. Lewis-type basic sites of higher strength and accessibility are thus created. The nature of the solvent mainly acts through its acidity able to poison the basic sites of the nanocatalysts.

Ce-Containing MgAl-Layered Double Hydroxide-Graphene Oxide Hybrid Materials as Multifunctional Catalysts for Organic Transformations

“…As it can be observed, the crystallite sizes, in particular the coherence lengths in the layer-stacking direction (D 003 ), were affected by the presence of GO. Indeed, the incorporation of GO led to the formation of larger LDH particles suggesting the involvement of the GO sheets as nucleating agents for the LDH phase formation [ 50 ]. The evolution in the HT3Ce-xGO series of the absolute intensities of the (110) line, exclusively related to the brucite-like layer, should go along with the decrease of the proportion of the LDH phase in the nanocomposites.…”

Layered Double Hydroxide/Nanocarbon Composites as Heterogeneous Catalysts: A Review

“…GO is produced via oxidative exfoliation of graphite using the Hummers or modified Hummers method [27]. The functionalized surface of GO allows the nucleation and growth of LDH by electrostatic forces between GO and the LDH cation precursors [20,21,32,33,[37][38][39][40]. Treatment of GO with citric acid (CA) leads to hierarchical LDH/GO composites containing completely exfoliated GO, supporting small LDH particles vertically oriented, due to the complexation effect of citrate on the LDH nucleation sites [35,39,41].…”

“…Coprecipitation of LDH on the nanocarbon has been performed following different approaches. The metal precursor salts of the LDH can be added to the carbon material (GO, functionalized CNT, CD) with subsequent addition of the alkaline solution [20,37,38,47,49]. When LDH is precipitated on CNT, the particles nucleate and grow within the open framework of CNT, as well as separated domains.…”

“…A series of publications reported the use of MgAl-LDH NPs deposited on various nanocarbons (CNF, MWCNT, or GO) as solid base catalysts for the self-condensation of acetone, the single-stage synthesis of MIBK, the Claisen-Schmidt condensation of acetophe-none and benzaldehyde, the Knoevenagel reaction, and the transesterification of glycerol with diethyl carbonate [13,14,20,37,44,[59][60][61].…”

The Influence of the Preparation Method on the Physico-Chemical Properties and Catalytic Activities of Ce-Modified LDH Structures Used as Catalysts in Condensation Reactions

“…Similarly, flavone (FL) is considered the “backbone” of many compounds used to treat numerous diseases. The literature on this topic indicates that various LDH compositions were tested as catalysts for chalcone and flavone synthesis via the Claisen–Schmidt condensation reaction [ 24 , 25 , 26 ]. Still, no studies have referred to the usage of LDH-type compounds modified with cerium until now.…”