Evidence for Copper Dimers in Low-Loaded CuOx/SiO2 Catalysts for Cyclohexane Oxidative Dehydrogenation

Scott L. Nauert, Andrew S. Rosen, Hacksung Kim, Randall Q. Snurr, Peter C Stair, Justin M Notestein

Research output: Contribution to journalArticle

2 Citations (Scopus)

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 languageEnglish
Pages (from-to)9775-9789
Number of pages15
JournalACS Catalysis
Volume8
Issue number10
DOIs
Publication statusPublished - Oct 5 2018

Fingerprint

Copper oxides
Dehydrogenation
Cyclohexane
Dimers
Copper
Catalysts
X ray absorption
Silicon Dioxide
Silica
Siloxanes
Oxidation
Catalyst selectivity
Catalyst supports
Impregnation
Calcination
Catalysis
Density functional theory
Catalyst activity
Drying
Spectroscopy

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

Cite this

Evidence for Copper Dimers in Low-Loaded CuOx/SiO2 Catalysts for Cyclohexane Oxidative Dehydrogenation. / Nauert, Scott L.; Rosen, Andrew S.; Kim, Hacksung; Snurr, Randall Q.; Stair, Peter C; Notestein, Justin M.

In: ACS Catalysis, Vol. 8, No. 10, 05.10.2018, p. 9775-9789.

Research output: Contribution to journalArticle

Nauert, Scott L. ; Rosen, Andrew S. ; Kim, Hacksung ; Snurr, Randall Q. ; Stair, Peter C ; Notestein, Justin M. / Evidence for Copper Dimers in Low-Loaded CuOx/SiO2 Catalysts for Cyclohexane Oxidative Dehydrogenation. In: ACS Catalysis. 2018 ; Vol. 8, No. 10. pp. 9775-9789.
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