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Acid site densities could be reversibly tuned by a factor of ∼30 using an O2 co-feed, which reversibly creates Brønsted acid sites on the carbide surface without altering the bulk crystal structure of 2-5 nm Mo2C crystallites. Unimolecular isopropanol (IPA) dehydration at 415 K, a probe reaction, occurred on Brønsted acid sites of these oxygen-modified carbides with an intrinsic activation energy of 93 ± 1.3 kJ mole-1 via an E2 elimination mechanism with a kinetically-relevant step of β-hydrogen scission. Site densities were estimated via in situ 2,6-di-tert-butylpyridine (DTBP) titration and used to calculate a turnover frequency (TOF) of 0.1 s-1, which was independent of site density. Oxygen co-processing allows for facile in situ tunability of acidic and metallic sites on highly oxophilic metal carbides.
Bibliographical noteFunding Information:
This research was supported by Office of Basic Energy Sciences, the U.S. Department of Energy under award number no. DE-SC0008418 (DOE Early Career Program). Partial support was also provided by the MRSEC program of the National Science Foundation under Award Number DMR-1420013. Part of this work was carried out in the College of Science and Engineering Characterization Facility, University of Minnesota, which has received capital equipment funding from the NSF through the MRSEC program. We thank Ms. Linda Sauer and Javier Garcia Barriocanal for assistance with the X-ray diffraction studies. We also thank Dr. Bing Luo for assistance with the X-ray photoelectron spectroscopy studies.
© 2015 Elsevier B.V. All rights reserved.
- Bifunctional catalyst
- Brønsted acid
- Interstitial carbide
- Molybdenum carbide
- Site density
- Transition metal
How much support was provided by MRSEC?
Reporting period for MRSEC
- Period 3