Formation of a Porous Crystalline MgAlO Overlayer on Metal Catalysts via Controlled Solid-State Reactions for High-temperature Stable Catalysis.

Catalyst deactivation by sintering and coking is a long-standing issue in metal-catalyzed harsh high-temperature hydrocarbon reactions. Ultrathin oxide coatings of metal nanocatalysts have recently appeared attractive to address this issue, while the porosity of the overlayer is difficult to control to preserve the accessibility of embedded metal nanoparticles, thus often leading to a large decrease in activity. Here, we report that a nanometer-thick alumina coating of MgAlO-supported metal catalysts followed by high-temperature reduction can transform a nonporous amorphous alumina overlayer into a porous MgAlO crystalline spinel structure with a pore size of 2-3 nm and weakened acidity. The high porosity stems from the restrained Mg migration from the MgAlO support to the alumina overlayer through solid-state reactions at high temperatures. The resulting Ni/MgAlO and Pt/MgAlO catalysts with a porous crystalline MgAlO overlayer achieved remarkably high stability while preserving much higher activity than the corresponding alumina-coated Ni and Pt catalysts on MgO and AlO supports in the reactions of dry reforming of methane and propane dehydrogenation, respectively.