Abstract
Copper oxide catalysts supported on KIT-6 silica were evaluated for cyclohexane oxidative dehydrogenation (ODH) to determine the effects of copper oxide domain size on ODH activity and selectivity. The catalysts were prepared by incipient wetness impregnation of KIT-6 at copper surface densities spanning 0.01-0.7 Cu/nm2 with carefully controlled drying and calcination conditions to systematically vary the average local copper oxide domain size. A distinct copper oxide active site exhibiting an order of magnitude higher activity than large copper oxide domains was identified by model cyclohexane ODH studies coupled with in situ X-ray absorption and UV-visible spectroscopies during reduction in H2. The structure of this site is experimentally identified by a combination of extended X-ray absorption fine structure analysis, resonant Raman studies, and modeling by density functional theory. All constraints imposed by these techniques indicate the active site is a mono(μ-oxo)dicopper(II) structure with copper sited in 4-member rings formed by copper insertion into highly strained 3-member siloxane ring defects which form on dehydrated silica. Given the ubiquity of copper oxide sites in selective oxidation catalysis, the understanding of such structures may prove relevant for other oxidation reactions.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 9775-9789 |
| Number of pages | 15 |
| Journal | ACS Catalysis |
| Volume | 8 |
| Issue number | 10 |
| DOIs | |
| State | Published - Oct 5 2018 |
Funding
This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1324585. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DOE DE-FG02-03-ER154757. Portions of this work were performed with the valuable assistance of Dr. Qing Ma at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by Northwestern University, E.I. DuPont de Nemours & Co., and The Dow Chemical Company. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This work made use of the J.B. Cohen X-ray Diffraction Facility supported by the MRSEC program of the National Science Foundation (DMR-1121262) at the Materials Research Center of Northwestern University and the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205). This work made use of the IMSERC at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the State of Illinois, and International Institute for Nanotechnology (IIN). Metal analysis was performed at the Northwestern University Quantitative Bioelement Imaging Center. The Raman work at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Basic Energy Sciences Contract No. DE-AC02-06CH11357. H.K. acknowledges the financial support from the R&D Convergence Program of MSIP (Ministry of Science, ICT and Future Planning) and NST (National Research Council of Science & Technology) of Republic of Korea (CRC-14-1-KRICT). A.S.R. acknowledges Government support under contract FA9550-11-C-0028 and awarded by the Department of Defense, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a. The authors acknowledge computing support through the resources and staff contributions provided for the Quest high-performance computing facility at Northwestern University.
ASJC Scopus subject areas
- Catalysis
- General Chemistry