Formation of a Porous Crystalline Mg 1-x Al 2 O y 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 MgAl 2 O 4 -supported metal catalysts followed by high-temperature reduction can transform a nonporous amorphous alumina overlayer into a porous Mg 1-x Al 2 O 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 MgAl 2 O 4 support to the alumina overlayer through solid-state reactions at high temperatures. The resulting Ni/MgAl 2 O 4 and Pt/MgAl 2 O 4 catalysts with a porous crystalline Mg 1-x Al 2 O y overlayer achieved remarkably high stability while preserving much higher activity than the corresponding alumina-coated Ni and Pt catalysts on MgO and Al 2 O 3 supports in the reactions of dry reforming of methane and propane dehydrogenation, respectively.