4.8 Article

Identification of a Pt3Co Surface Intermetallic Alloy in Pt-Co Propane Dehydrogenation Catalysts

Journal

ACS CATALYSIS
Volume 9, Issue 6, Pages 5231-5244

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acscatal.9b00549

Keywords

alkane dehydrogenation; bimetallic Pt-Co catalysts; in situ EXAFS analysis of Pt-Co nanoparticles; synchrotron nanoparticle X-ray diffraction of Pt-Co nanoparticle; intermetallic Pt-Co alloy formation; bimetallic nanoparticle surface structure determination

Funding

  1. Ciencias sem Fronteiras (Science without Borders)
  2. Brazilian governmental organization Conselho Nacional de Pesquisa (CNPq)
  3. Laspau [222473/2014]
  4. National Science Foundation [EEC-1647722]
  5. Fundamental Research Funds for the Central Universities [DUT18RC(3) 057]
  6. U.S. Department of Energy, Office of Basic Energy Sciences [DE-AC02-06CH11357]

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Bimetallic Pt-Co nanoparticles (NPs) were prepared and characterized by scanning transmission electron microscopy, in situ X-ray absorption spectroscopy, in situ synchrotron X-ray diffraction, and catalytic conversion for propane dehydrogenation with and without added H-2. In addition, the surface extended X-ray absorption fine structure (EXAFS) obtained by fitting the difference spectrum between the fully reduced and room-temperature-oxidized catalysts suggest that the surface structure remains Pt3Co, although the core changes from Pt to Pt3Co and to PtCo. At low Co loading, the bimetallic nanoparticles form a Pt3Co intermetallic surface alloy with Pt-rich core. With increasing Co loading, a full alloy forms where both the surface and NP compositions are Pt3Co. A further increase in Co loading leads to a Co-rich NP core, likely PtCo, with a surface of Pt3Co. Although Pt-Co intermetallic alloys form two different phases and several morphologies, the surface structures are similar in all catalysts. Although both monometallic Pt and Co are active for alkane dehydrogenation, all bimetallic Pt-Co catalysts are significantly more olefin selective than either single metal. The turnover rates of the bimetallic catalysts indicate that Pt is the active atom with little contribution from Co atoms. The high olefin selectivity is suggested to be due to Co acting as a less active structural promoter to break up large Pt ensembles in bimetallic NPs.

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