Core-shell nanocatalysts stretch out noble metals

The high cost of noble metals often drives researchers to seek more efficient ways of using them to make catalysts for applications such as fuel cells and catalytic converters. One team’s effort has led to a procedure for preparing nanoparticle catalysts consisting of an atomically thin noble-metal shell wrapped around an inexpensive metal-carbide core (Science 2016, DOI: 10.1126/science.aad8471). Sean T. Hunt and Yuriy Román-Leshkov of MIT and coworkers treated tungsten oxide nanoparticles with (NH₄)₂PtCl₆ and encapsulated the particles with silica nanospheres. They then subjected the material to a mixture of methane and hydrogen while gradually raising the temperature to 900 °C. At the lowest temperatures, platinum nanoclusters formed on tungsten oxide. As things heated up, the surface material transitioned into mixtures of platinum and tungsten and then to platinum and tungsten carbide. Because noble metals are insoluble in transition-metal carbides, the platinum segregated and formed a shell around a tungsten carbide core. The team also devised mixed-metal shells and cores. Methanol electrooxidation tests show that platinum-ruthenium- and Pt-coated tungsten titanium carbide catalysts are more stable and 10 times as active as current commercial catalysts.