TY - JOUR
T1 - Structural and electronic promotion with alkali cations of silica-supported Fe(III) sites for alkane oxidation
AU - Prieto-Centurion, Dario
AU - Boston, Andrew M.
AU - Notestein, Justin M.
N1 - Funding Information:
J.M.N. acknowledges support from U.S. Department of Energy-Office of Basic Energy Sciences grant DE-SC0006718, Northwestern University, and a 3M Non-Tenured Faculty Grant. DPC acknowledges the support of Toyota Motor Engineering, Inc. and thanks Dr. Christian Canlas, Pria Young, and Todd Eaton for the helpful discussions. Portions of this work were performed with the valuable help 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 E.I. DuPont de Nemours & Co., The Dow Chemical Company and Northwestern University. Use of the APS, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357.
PY - 2012/12
Y1 - 2012/12
N2 - Promoters and precursors can control oxide phase, dispersion, and per-site reactivity of supported oxide catalysts. Previously, dispersed FeOx-SiO 2 resulted from Fe3+ ethylenediaminetetraacetate (FeEDTA-) precursors, with NaFeEDTA giving enhanced dispersion and oxidation rates vs. NH4FeEDTA. Here, catalysts were synthesized by sequential alkali deposition and Fe3+ impregnation. At up to 0.9 Fe nm-2 from NH4FeEDTA and equimolar alkali, UV-visible and H2 TPR were consistent with isolated Fe3+ and small FeOx clusters. Omitting alkali, using Fe(NO3)3, or using Fe/alkali >1 gave evidence of larger agglomerates. For Fe/alkali ≤1 on non-porous SiO2, initial turnover frequencies in adamantane oxidation using H2O2 were independent of surface density. TOF increased as 6.3, 8.8, 15.4, and 20.9 (±0.3) ks-1 for Li +, Na+, K+, and Cs+, respectively, increasingly linearly with decreasing electronegativity. These results give a synthesis-structure-function taxonomy with alkali as an electronic and structural promoter of dispersed FeOx species for alkane selective oxidation.
AB - Promoters and precursors can control oxide phase, dispersion, and per-site reactivity of supported oxide catalysts. Previously, dispersed FeOx-SiO 2 resulted from Fe3+ ethylenediaminetetraacetate (FeEDTA-) precursors, with NaFeEDTA giving enhanced dispersion and oxidation rates vs. NH4FeEDTA. Here, catalysts were synthesized by sequential alkali deposition and Fe3+ impregnation. At up to 0.9 Fe nm-2 from NH4FeEDTA and equimolar alkali, UV-visible and H2 TPR were consistent with isolated Fe3+ and small FeOx clusters. Omitting alkali, using Fe(NO3)3, or using Fe/alkali >1 gave evidence of larger agglomerates. For Fe/alkali ≤1 on non-porous SiO2, initial turnover frequencies in adamantane oxidation using H2O2 were independent of surface density. TOF increased as 6.3, 8.8, 15.4, and 20.9 (±0.3) ks-1 for Li +, Na+, K+, and Cs+, respectively, increasingly linearly with decreasing electronegativity. These results give a synthesis-structure-function taxonomy with alkali as an electronic and structural promoter of dispersed FeOx species for alkane selective oxidation.
KW - Alkali promoters
KW - EDTA ligand
KW - High dispersion
KW - Single-site catalyst
KW - Supported oxide
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U2 - 10.1016/j.jcat.2012.09.004
DO - 10.1016/j.jcat.2012.09.004
M3 - Article
AN - SCOPUS:84871290627
SN - 0021-9517
VL - 296
SP - 77
EP - 85
JO - Journal of Catalysis
JF - Journal of Catalysis
ER -