Multimetal Layered Double Hydroxides: Synthesis, Characterization, and Synergic Effect in Mild Catalytic Oxidation of Alkanes

Abstract

Layered double hydroxides (LDHs) represent a promising class of inexpensive and tunable inorganic materials with growing applications in diverse areas. In this study, we applied an aqueous miscible organic solvent treatment (AMOST) to prepare a novel series of highly dispersed LDHs containing up to four different metal centers (Mg, Cu, Al, and Fe). These AMO-LDHs were fully characterized and employed as precatalysts for the mild oxidative functionalization of cyclic and gaseous alkanes with aqueous H₂O₂ to give the corresponding alcohols, ketones, and carboxylic acids. Cyclohexane and propane were used as model substrates. The oxidation reactions, occurring under mild conditions (30–50 °C), demonstrated good efficiency with total product yields up to 40% and catalyst turnover numbers up to 370 when using a tetra-heterometallic AMO-LDH precatalyst (AMO-MgCuAlFe). Its enhanced catalytic activity is likely associated with the synergic effect of different metal centers (Cu, Fe, and Al─all having a recognized function in oxidation catalysis). Substrate scope, selectivity, and the influence of the reaction parameters were also investigated. This work offers a novel, easy, and more sustainable path to advance the application of AMO-LDHs in oxidation catalysis, opening up the use of this type of catalytic systems in the mild oxidation of alkanes.