Eric J. Peterson

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

Hot single-atom catalysts For heterogeneous catalysts made from precious metal nanoparticles adsorbed on metal oxides, high temperatures are the enemy. The metal atoms become mobile and the small particles grow larger, causing a loss in surface area and hence in activity. Jones et al. turned this process to their advantage and used these mobile species to create single-atom platinum catalysts. The platinum on alumina supported transfers in air at 800°C to ceria supports to form highly active catalysts with isolated metal cations. Science, this issue p. 150 Exposure of a ceria support to mobile platinum species at high temperatures traps single atoms at the most stable sites. 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.

Low-temperature carbon monoxide oxidation catalysed by regenerable atomically dispersed palladium on alumina

Catalysis by single isolated atoms of precious metals has attracted much recent interest, as it promises the ultimate in atom efficiency. Most previous reports are on reducible oxide supports. Here we show that isolated palladium atoms can be catalytically active on industrially relevant γ-alumina supports. The addition of lanthanum oxide to the alumina, long known for its ability to improve alumina stability, is found to also help in the stabilization of isolated palladium atoms. Aberration-corrected scanning transmission electron microscopy and operando X-ray absorption spectroscopy confirm the presence of intermingled palladium and lanthanum on the γ-alumina surface. Carbon monoxide oxidation reactivity measurements show onset of catalytic activity at 40 °C. The catalyst activity can be regenerated by oxidation at 700 °C in air. The high-temperature stability and regenerability of these ionic palladium species make this catalyst system of potential interest for low-temperature exhaust treatment catalysts.

Hierarchically Structured Pt–Alloy Ethanol Oxidation Electrocatalysts

Bimodal-sized Pt–Sn and Ru–alloy catalysts for the electro-oxidation of ethanol were synthesized using a novel templating approach and evaluated for ethanol oxidation in alkaline media. This templating approach leads to trimodal-sized catalyst particles embedded in and on bimodal-pore carbon support. Electrochemical evaluation suggested that Pt–Sn phases enhance dehydrogenation and/or C–C bond splitting, while Pt–Ru phases facilitates complete oxidation of the intermediate reaction product CO. The criteria for best-performing catalyst are derived from studies and found to be 2–5xa0nm Pt(Sn) and the addition of Ru is conjectured to be beneficial. Mass transport effects observed demonstrates that it is possible to effect catalytic performance using the hierarchically structured templating approach used.

Metal–Organic Framework (MOF) Nanorods, Nanotubes, and Nanowires

New mechanisms for the controlled growth of one-dimensional (1D) metal-organic framework (MOF) nano- and superstructures under size-confinement and surface-directing effects have been discovered. Through applying interfacial synthesis templated by track-etched polycarbonate (PCTE) membranes, congruent polycrystalline zeolitic imidazolate framework-8 (ZIF-8) solid nanorods and hollow nanotubes were found to form within 100u2005nm membrane pores, while single crystalline ZIF-8 nanowires grew inside 30u2005nm pores, all of which possess large aspect ratios up to 60 and show preferential crystal orientation with the {100} planes aligned parallel to the long axis of the pore. Our findings provide a generalizable method for controlling size, morphology, and lattice orientation of MOF nanomaterials.

Designing Catalysts for Meeting the DOE 150 °C Challenge for Exhaust Emissions

1. Department of Chemical and Biological Engineering and Center for Micro-Engineered Materials, University of New Mexico, Albuquerque, NM, USA. 2. General Motors Global R&D, 30500 Mound Road, Warren, MI, USA. 3. Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, USA. 4. Institute for Integrated Catalysis, Pacific Northwestern National Laboratory, Richland, WA, USA.

Design of Effective Catalysts for Selective Alkyne Hydrogenation by Doping of Ceria with a Single-Atom Promotor

Since the discovery that ceria is an active catalyst for selective hydrogenation of alkynes, there has been much debate on the catalytic mechanism. In this work, we propose, based on density functional theory (DFT) investigations, a mechanism that involves the heterolytic dissociation of H2 at oxygen vacancies of CeO2(111), facilitated by frustrated Lewis pairs consisting of spatially separated O and Ce sites. The resulting O-H and Ce-H species effectively catalyze the hydrogenation of acetylene, avoiding the overstabilization of the C2H3* intermediate in a previously proposed mechanism. On the basis of our mechanism, we propose the doping of ceria by Ni as a means to create oxygen vacancies. Interestingly, the Ni dopant is not directly involved in the catalytic reaction, but serves as a single-atom promoter. Experimental studies confirm the design principles and demonstrate much higher activity for Ni-doped ceria in selective hydrogenation of acetylene. The combined results from DFT calculations and experiment provide a basis to further develop selective hydrogenation catalysts based on earth-abundant materials.