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Title: Silica-Supported, Single-Site Sc and Y Alkyls for Catalytic Hydrogenation of Propylene

Single site Sc and Y on silica catalysts have been prepared by aqueous and organometallic grafting methods. The former yields Y(III) ions with 5 bonds at an average bond distance of 2.31 Å by X-ray absorption spectroscopy. Although the aqueous synthesis gave single site Y with low coordination number, these were not catalytic for alkane dehydrogenation or olefin hydrogenation. Single site Sc(III) and Y(III) species were also prepared by grafting Sc(CH 2Si(CH 3) 3) 3(THF) 2 and Y(CH 2Si(CH 3) 3) 3(THF) 2, respectively and these are catalysts for olefin hydrogenation at temperatures from about 60 to 100°C; however, they were thermally unstable at higher temperatures necessary for alkane dehydrogenation. The structure of the grafted Y complex was determined by X-ray absorption spectroscopy, IR, and NMR. Grafting lead to protonolysis of 2 of the 3 CH 2Si(CH 3) 3 ligands. Additionally, there was loss of one THF ligand. The EXAFS indicated that there were 4 Y-ligand bonds in the surface species, 2 at 2.16 Å and 2 at 2.39 Å. The metal-alkyl ligand was thought to be necessary for catalytic activity and likely proceeds through a sigma bond metathesis mechanism. In the single site centers without alkyl bonds, Sc andmore » Y ions cannot generate metal-alkyl, or metal-hydride, moieties in situ. We conclude that this is likely due to the very high M-O-Si bond strengths, which must be broken through heterolytic dissociation of C-H bonds during alkane activation for either alkane dehydrogenation or olefin hydrogenation reactions. Lastly, this study demonstrates the importance of pre-catalyst choice versus in situ formation of reactive intermediates to produce active catalysts for alkane bond activation.« less
 [1] ;  [2] ;  [3] ; ORCiD logo [4]
  1. Argonne National Lab. (ANL), Lemont, IL (United States)
  2. Illinois Inst. of Technology, Chicago, IL (United States)
  3. Argonne National Lab. (ANL), Lemont, IL (United States); Purdue Univ., West Lafayette, IN (United States)
  4. Argonne National Lab. (ANL), Lemont, IL (United States); Illinois Inst. of Technology, Chicago, IL (United States)
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Accepted Manuscript
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Additional Journal Information:
Journal Volume: 36; Journal Issue: 19; Journal ID: ISSN 0276-7333
American Chemical Society
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; single site Sc catalyst; grafted Sc(III) alkyl hydrogenation catalyst; grafted Y(III) alkyl hydrogenation catalyst; single site Y catalyst
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