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

Journal Article · Wed Sep 27 00:00:00 EDT 2017 · Organometallics

DOI:https://doi.org/10.1021/acs.organomet.6b00623· OSTI ID:1400402

Getsoian, Andrew G. Bean ^[1]; Hu, Bo ^[2]; Miller, Jeffrey T. ^[3]; Hock, Adam S.  ^[4]

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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)

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(CH₂Si(CH₃)₃)₃(THF)₂ and Y(CH₂Si(CH₃)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 CH₂Si(CH₃)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 and 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.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1400402
• Journal Information: Organometallics, Vol. 36, Issue 19; ISSN 0276-7333
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

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