Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al2O3, likely stabilized by coordinatively unsaturated pentahedral Al3+ centres. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atmosphere at 200 °C for 24 h. Compared to commercial Pt nanoparticle catalyst on Al2O3 and control samples, this system exhibits significantly enhanced stability and performance for n-hexane hydro-reforming at 550 °C for 48 h, although agglomeration of Pt single-atoms into clusters is observed after reaction. In CO oxidation, the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 °C over a one-month period.
Despite significant advances in the fabrication and applications of graphene-like materials, it remains a challenge to prepare single-layered metallic materials, which have great potential applications in physics, chemistry and material science. Here we report the fabrication of poly(vinylpyrrolidone)-supported single-layered rhodium nanosheets using a facile solvothermal method. Atomic force microscope shows that the thickness of a rhodium nanosheet is o4 Å. Electron diffraction and X-ray absorption spectroscopy measurements suggest that the rhodium nanosheets are composed of planar single-atom-layered sheets of rhodium. Density functional theory studies reveal that the single-layered Rh nanosheet involves a d-bonding framework, which stabilizes the single-layered structure together with the poly(vinylpyrrolidone) ligands. The poly(vinylpyrrolidone)-supported single-layered rhodium nanosheet represents a class of metallic two-dimensional structures that might inspire further fundamental advances in physics, chemistry and material science.
In coordination chemistry, catalytically active metal complexes in a zero- or low-valent state often adopt four-coordinate square-planar or tetrahedral geometry. By applying this principle, we have developed a stable Pt1 single-atom catalyst with a high Pt loading (close to 1 wt %) on phosphomolybdic acid(PMA)-modified active carbon. This was achieved by anchoring Pt on the four-fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square-planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities.
In this paper, NiRu, NiRh, and NiPd catalysts were synthesized and evaluated in the hydrogenolysis of lignin C− O bonds, which is proved to be superior over single-component catalysts. The optimized NiRu catalyst contains 85% Ni and 15% Ru, composed of Ni surface-enriched, Ru−Ni atomically mixed, ultrasmall nanoparticles. The Ni 85 Ru 15 catalyst showed high activity under low temperature (100 °C), low H 2 pressure (1 bar) in β-O-4 type C−O bond hydrogenolysis. It also exhibited significantly higher activity over Ni and Ru catalysts in the direct conversion of lignin into monomeric aromatic chemicals. Mechanistic investigation indicates that the synergistic effect of NiRu can be attributed to three factors: (1) increased fraction of surface atoms (compared with Ni), (2) enhanced H 2 and substrate activation (compared with Ni), and (3) inhibited benzene ring hydrogenation (compared with Ru). Similarly, NiRh and NiPd catalysts were more active and selective than their singlecomponent counterparts in the hydrogenolysis of lignin model compounds and real lignin.
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