Abstract
Mixed oxides are ubiquitious solid acid catalysts for a number of transformations. Here, the chemistry of mixed oxide interfaces was experimentally probed by constructing model SiO2 on MOx interfaces using a liquid-phase, stoichiometrically-controlled deposition of tetraethyl orthosilicate (TEOS). Catalytically active Brønsted sites were generated in four series of overcoated SiO2 on metal oxide materials prepared by depositing TEOS onto Al2O3, anatase TiO2, Nb2O5, and ZrO2. Pyridine DRIFTS studies indicate that the acidity of deposited silanol groups was enhanced by interaction with the metal oxide surface, suggesting that pseudo-bridging silanol type structures were formed. Trimethylphosphine oxide (TMPO) 31P NMR experiments showed that Brønsted acid strength varied in the overcoated materials, with increasing strength in the following order: SiO2/ZrO2 < SiO2/TiO2 < SiO2/Nb2O5 < SiO2/Al2O3. This order correlated with the Lewis acidity and chemical hardness of the underlying metal oxides. The catalytic performance of the materials was evaluated in the liquid-phase hydroalkoxylation of dihydropyran with n-octanol, revealing that activity was highly dependent on SiO2 loading, which impacted the density of acid sites, and scaled exponentially with Brønsted acid strength, determined by the core metal oxide identity. Brønsted acid strength appears to be the key driver of the materials’ activity, with the highest areal rate of 2.2 mmol / m2 – h being measured over SiO2/Al2O3. This study shows that SiO2-overcoated materials are a systematically tunable class of catalysts that can be applied to acid catalyzed reactions.
Original language | English (US) |
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Pages (from-to) | 113-125 |
Number of pages | 13 |
Journal | Journal of Catalysis |
Volume | 426 |
DOIs | |
State | Published - Oct 2023 |
Funding
This material is primarily based upon work supported by the National Science Foundation under Cooperative Agreement No. EEC-1647722 for support of A.T.Y.W. Funding from the Department of Energy, Office of Science, Basic Energy Sciences under award number DE-SC0012702 supported TMPO 31 P MAS SS-NMR experiments conducted by K.E.H. Metal analysis was performed at the Northwestern University Quantitative Bio-element Imaging Center. This work made use of the EPIC facility of Northwestern’s University’s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. This work made use of the Jerome B. Cohen X-Ray Diffraction Facility supported by the MRSEC program of the National Science Foundation (DMR-1720139) at the Materials Research Center of Northwestern University and the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205). The REACT Core facility acknowledges funding from the Department of Energy (DE-FG02-03ER15457) used for the purchase of the Altamira AMI-200 and the Nicolet 6700 FT-IR.
Keywords
- Brønsted acids
- Hydroalkoxylation
- Mixed oxides
- Overcoated materials
- Tetrahydropyranylation
ASJC Scopus subject areas
- Catalysis
- Physical and Theoretical Chemistry