Formation of a Porous Crystalline Mg1‐xAl2Oy 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 MgAl₂O₄-supported metal catalysts followed by high-temperature reduction can transform a nonporous amorphous alumina overlayer into a porous Mg_1-xAl₂O_y 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 MgAl₂O₄ support to the alumina overlayer through solid-state reactions at high temperatures. The resulting Ni/MgAl₂O₄ and Pt/MgAl₂O₄ catalysts with a porous crystalline Mg_1-xAl₂O_y overlayer achieved remarkably high stability while preserving much higher activity than the corresponding alumina-coated Ni and Pt catalysts on MgO and Al₂O₃ supports in the reactions of dry reforming of methane and propane dehydrogenation, respectively.