Catalysts based on single atoms of scarce precious metals can lead to more efficient use through enhanced reactivity and selectivity. However, single atoms on catalyst supports can be mobile and aggregate into nanoparticles when heated at elevated temperatures. High temperatures are detrimental to catalyst performance unless these mobile atoms can be trapped. We used ceria powders having similar surface areas but different exposed surface facets. When mixed with a platinum/aluminum oxide catalyst and aged in air at 800°C, the platinum transferred to the ceria and was trapped. Polyhedral ceria and nanorods were more effective than ceria cubes at anchoring the platinum. Performing synthesis at high temperatures ensures that only the most stable binding sites are occupied, yielding a sinter-resistant, atomically dispersed catalyst.

Thermally stable single-atom platinum-on-ceria catalysts via atom trapping

Surface-supported isolated atoms in single-atom catalysts (SACs) are usually stabilized by diverse defects. The fabrication of high-metal-loading and thermally stable SACs remains a formidable challenge due to the difficulty of creating high densities of underpinning stable defects. Here we report that isolated Pt atoms can be stabilized through a strong covalent metal-support interaction (CMSI) that is not associated with support defects, yielding a high-loading and thermally stable SAC by trapping either the already deposited Pt atoms or the PtO2 units vaporized from nanoparticles during high-temperature calcination. Experimental and computational modeling studies reveal that iron oxide reducibility is crucial to anchor isolated Pt atoms. The resulting high concentrations of single atoms enable specific activities far exceeding those of conventional nanoparticle catalysts. This non defect-stabilization strategy can be extended to non-reducible supports by simply doping with iron oxide, thus paving a new way for constructing high-loading SACs for diverse industrially important catalytic reactions.

Non defect-stabilized thermally stable single-atom catalyst

Catalysis and combustion have long been linked. In fact, the science of catalysis stems from Davy's discovery [1] that platinum wires could promote the flameless combustion of flammable fuel-air mixtures. Today, catalysis is a mainstay of our modern chemical industry. Oxidation catalysts are used not only for the complete oxidation of fuels to carbon dioxide and water, as in radiant catalytic tent heaters and fume abatement devices, but also for the selective partial oxidation of hydrocarbons or other “fuels” to produce basic chemicals such as ethylene oxide (from ethylene), terephthalic acid (from p-xylene), and nitric acid (from ammonia). However, despite the long-known capability of catalysts to oxidize hydrocarbons without significant production of carbon monoxide, soot, or thermal NOx, there seemed little possibility that catalytic oxidation reactors could ever displace conventional flame combustors as primary fuel combustors. This is because the volumetric heat release rates of conventional...

Catalysis in Combustion

Ultrapurification of water for electrochemical and surface chemical work by catalytic pyrodistillation

Foreword. List of abbreviations. Introduction. Reactor materials and fission products. Data assessment. Construction of the tables. Fundamental constants. Nomenclature and symbols. References. Americium. Barium. Boron. Caesium. Europium. Hydrogen. Iodine. Krypton. Lanthanum. Molybdenum. Neodymium. Oxygen. Palladium. Plutonium. Rhodium. Ruthenium. Sodium. Strontium. Technetium. Tellurium. Tin. Uranium. Xenon. Zirconium. Tables. Index of Tables.

Thermochemical Data for Reactor Materials and Fission Products

The oxide species responsible for the enhanced volatility of platinum and rhodium in oxygen in the temperature range 1000 to 1600 °C have been elucidated, and the thermodynamics of their formation have been calculated from their vapour pressures, which were measured by means of the ‘transportation’ or ‘carrier gas’ technique. Similar, but incomplete, studies have been made on the metals ruthenium, iridium and palladium, and thermodynamic data have been calculated for the proposed oxide species.

G. W. : Hooper

Papers

Thermodynamics of the Gaseous Oxides of the Platinum-Group Metals