期刊
NANO LETTERS
卷 13, 期 10, 页码 4893-4901出版社
AMER CHEMICAL SOC
DOI: 10.1021/nl402768b
关键词
Nanoparticles; sulfidation; thiol; catalysis; sulfur poisoning; palladium
类别
资金
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility [DE-AC02-06CH11357]
- U.S. Department of Energy-Basic Energy Sciences
- NSERC
- University of Washington
- Canadian Light Source and the Advanced Photon Source [DE-AC02-06CH11357]
- University of Chicago MRSEC
- NSF [DMR-0820054]
- Exxon Mobil
A significant issue related to Palladium (Pd) based catalysts is that sulfur-containing species, such as alkanethiols, can form a PdSx underlayer on nanoparticle surface and subsequently poison the catalysts. Understanding the exact reaction pathway, the degree of sulfidation, the chemical stoichiometry, and the temperature dependence of this process is critically important. Combining energy-filtered transmission electron microscopy (EFTEM), X-ray diffraction (XRD), and X-ray absorption spectroscopy experiments at the S K-, Pd K-, and L-2,L-3-edges, we show the kinetic pathway of Pd nanoparticle sulfidation process with the addition of excess amount of octadecanethiol at different temperatures, up to 250 degrees C. We demonstrate that the initial polycrystalline Pd-oleylamine nanoparticles gradually become amorphous PdSx nanoparticles, with the sulfur atomic concentration eventually saturating at Pd/S = 66:34 at 200 degrees C. This final chemical stoichiometry of the sulfurized nanoparticles closely matches that of the crystalline P16S7 phase (30.4% S), albeit being structurally amorphous. Sulfur diffusion into the nanoparticle depends strongly on the temperature. At 90 degrees C, sulfidation remains limited at the surface of nanoparticles even with extended heating time; whereas at higher temperatures beyond 125 degrees C, sulfidation occurs rapidly in the interior of the particles, far beyond what can be described as a core shell model. This indicates sulfur diffusion from the surface to the interior of the particle is subject to a diffusion barrier and likely first go through the grain boundaries of the nanoparticle.
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