(196e) Identification of Distinct Sn Sites in Siliceous Zeolites for Mpvo and C-C Bond Formation Catalysis

Lewis, J., Massachusetts Institute of Technology
Roman, Y., MIT

Identification of Distinct Sn Sites in Siliceous
Zeolites for MPVO and C-C Bond Formation Catalysis


John R. Di Iorio, Jennifer D. Lewis,and Yuriy

Department of Chemical Engineering, Massachusetts Institute
of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA


Lewis acidic Sn sites confined
within siliceous *BEA zeolites have garnered significant attention as catalysts
for oxygenate upgrading due to their high selectivity and stability for Meerwein-Ponndorf-Verley
reduction and Oppenauer oxidation (MPVO), Baeyer-Villiger oxidation (BVO), and
aldol condensation reactions in condensed media. IR spectra of Sn-*BEA zeolites
titrated with d3-acetonitrile (CD3CN) reveal two distinct
Lewis acidic Sn sites (ν = 2316 cm-1 and 2308 cm-1)
that have been assigned to partially-hydrolyzed open ((SiO)3-Sn-(OH))
and closed ((SiO)4-Sn) Sn sites, respectively, by a combination of 119Sn
magic-angle spinning (MAS) NMR [1] and DFT calculations [2]; the former of
which appears to be the active site for BVO [2] and glucose isomerization
reactions [3]. Moreover, 31P MAS NMR spectra of adsorbed
trimethylphosphine oxide (TMPO) on Sn-*BEA zeolites shows distinct 31P
chemical shifts for TMPO bound to different Sn sites that have been correlated with
rates of aldol condensation (δ ~ 58 ppm) and glucose isomerization (δ
~ 55 ppm) [4]. Here, we use IR spectra of adsorbed CD3CN and 31P
MAS NMR spectra of adsorbed TMPO to quantify the concentration of distinct Sn
sites on a series of hydrophobic, synthesized hydrothermally in F-media, and
hydrophilic, prepared via post-synthetic grafting of Sn into defective
frameworks, Sn-*BEA zeolites. Rates of glucose isomerization (373 K) and
benzaldehyde-acetone aldol condensation (383 K) are used to unify existing
observations regarding the catalytic role of different Sn sites quantified via ex-situ
CD3CN and TMPO site titrations. These results further highlight how
different Sn sites confined within siliceous *BEA zeolites facilitate distinct
chemical transformations important for the upgrading of biomass-derived


[1] Bermejo-Deval et al., ACS
, 2014, 4, 2288

[2] Boronat et al., J. Catal.,
2005, 234, 111

[3] Harris et al., J. Catal.,
2016, 335, 141

[4] Lewis et al., ACS Catal.,
2018, 8, 3076