Single-atom-catalyst (SAC), which we define as all the active metal species in a catalyst exist as isolated single atoms stabilized either by a support or by alloying with a second metal, is emerging as a new frontier of heterogeneous catalysis. With well-defined and uniform single-atom dispersion, SAC not only maximizes the atom utilization efficiency, but also offers new opportunities for achieving a high selectivity in selective oxidation and reduction reactions. In this presentation, we will demonstrate the concept and application of SAC in selective hydrogenation reactions. Two types of SACs are investigated. In the first type of SAC, Pt and Ir single atoms are stabilized by FeOx support. The resulting Pt1/FeOx and Ir1/FeOx SACs manifest outstanding chemoselectivity in the selective hydrogenation of nitroarenes to anilines. For hydrogenation of 3-nitrostyrene, the catalyst yields a TOF of 1500 h-1, 20-fold higher than the best result reported in literature, and a selectivity to 3-aminostyrene close to 99%, the best ever achieved over platinum group metals. The superior performance can be attributed to the presence of positively charged platinum centers and the absence of Pt-Pt metallic bonding, both of which favor the preferential adsorption of nitro groups. In the second type of SAC, Pd single atoms are obtained by forming single atom alloy with Au or Zn and sufficiently isolated by Au or Zn atoms. Density functional theory (DFT) calculations indicate that only the π-bonding pattern is feasible for ethylene adsorption on the isolated Pd active site but the moderate σ-bonding mode can be reserved for acetylene with two neighboring Pd sites, which would suppress the hydrogenation of ethylene. Catalytic performance results in the selective hydrogenation of acetylene demonstrate that Pd SAC possesses extraordinarily high selectivity towards ethylene with satisfying activity in the hydrogenation of acetylene.The strategy for and approach to tuning the desired properties of catalytically active centers by using SAC concept are general and can be broadened to other selective reactions involving hydrocarbon conversion.

Single-atom-catalysts: New opportunities in selective hydrogenation reactions

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.