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

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.