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

Abstract

Mechanical activation and mechanochemical reactions are the subjects of mechanochemistry, a special branch of chemistry studied intensively since the 19th century. Herein, we comparably describe two synthesis methods used to obtain the following layered double hydroxide doped with cerium, Mg3Al0.75Ce0.25(OH)8(CO3)0.5·2H2O: the mechanochemical route and the co-precipitation method, respectively. The influence of the preparation method on the physico-chemical properties as determined by multiple techniques such as XRD, SEM, EDS, XPS, DRIFT, RAMAN, DR-UV-VIS, basicity, acidity, real/bulk densities, and BET measurements was also analyzed. The obtained samples, abbreviated HTCe-PP (prepared by co-precipitation) and HTCe-MC (prepared by mechanochemical method), and their corresponding mixed oxides, Ce-PP (resulting from HTCe-PP) and Ce-MC (resulting from HTCe-MC), were used as base catalysts in the self-condensation reaction of cyclohexanone and two Claisen–Schmidt condensations, which involve the reaction between an aromatic aldehyde and a ketone, at different molar ratios to synthesize compounds with significant biologic activity from the flavonoid family, namely chalcone (1,3-diphenyl-2-propen-1-one) and flavone (2-phenyl-4H-1benzoxiran-4-one). The mechanochemical route was shown to have indisputable advantages over the co-precipitation method for both the catalytic activity of the solids and the costs.

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

“…A closer inspection of the grain surface revealed the presence of microparticles grouped either in polymorphic structures with sharp edges, “ovoidal” particles, or cubic agglomerates ( Figure 5 ). It is noteworthy that the morphology of the neat Ce-containing MgAl LDH sample was shown to be quite different [ 55 ], being described as assemblies of nanoplates nearly perpendicular to the outer surfaces of microspheres.…”

“…The higher activities of the hybrid HT3Ce-xGO systems compared to the neat HT3Ce catalyst could be due to their strong affinity for the organic substrate since graphene oxide presents a similar planar structure with the phenyl group. Moreover, the association of composite platelets in “ovoidal” particles in the hybrid materials, as evidenced in the SEM images ( Figure 5 ), could also be correlated with their enhanced activity compared to neat HT3Ce that shows no evident “ovoidal” particles [ 55 ].…”

Scanning Electron Microscopy and Raman Spectroscopy Characterization of Structural Changes Induced by Thermal Treatment in Innovative Bio-Based Polyamide Nanocomposites

“…Specifically, LDH material was previously evaluated in terms of its catalytic performance in specific reactions [36] or for co-precipitating the LDH phase in the presence of GO [37]. However, its behaviour in certain thermic conditions was not assessed, moreover in combination with a bio-PA1010.…”