TY - JOUR
T1 - Quantifying accessible sites and reactivity on titania-silica (photo)catalysts
T2 - Refining TOF calculations
AU - Eaton, Todd R.
AU - Campos, Michael P.
AU - Gray, Kimberly A.
AU - Notestein, Justin M.
N1 - Funding Information:
JMN acknowledges support from U.S. Department of Energy-Office of Basic Energy Sciences Grant DE-SC0006718 . KAG acknowledges the National Science Foundation for Grant CBET 0829146 . TRE acknowledges additional funding provided by the Initiative for Sustainability and Energy at Northwestern (ISEN) and thanks Dr. Christian Canlas and Dr. Dario Prieto-Centurion for their characterization assistance, as well as Michael Ackerson of Rensselaer Polytechnic Institute for supplying the fresnoite standard. This work made use of the J.B. Cohen X-ray Diffraction Facility supported by the Northwestern University Materials Research Science and Engineering Center (MRSEC) funded by NSF ( DMR-1121262 ). Portions of this work were performed with the valuable and patient 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. ICP-AES was performed in the Northwestern University Integrated Molecular Structure Education and Research Center (IMSERC) facilities at Northwestern University supported by NSF ( DMR-0114235 ).
PY - 2014
Y1 - 2014
N2 - It can be difficult to determine the number of active atoms accessible to the fluid phase in mixed oxide catalysts, as required for obtaining true turnover frequencies (TOF). Here, we utilize the selective titration of surface Ti atoms with phenylphosphonic acid (PPA) on TiO2-SiO2 materials to estimate the number of reactant-accessible sites. TiO 2-SiO2 composites were synthesized over a range of Ti loadings from grafting of titanocene dichloride (Cp2TiCl2) or tetraethoxy orthotitanate (TEOT) on SiO2 and sol-gel co-hydrolysis of Si and Ti alkoxides. The materials were characterized by DRUV-vis, XRD, BET, and XANES. Despite the significant morphological and electronic differences, materials prepared by Cp2TiCl2 and TEOT yielded a near-constant TOF of 0.14 h-1 (±0.04) across Ti loadings, for benzyl alcohol photooxidation, when normalizing rates by sites titrated by PPA. The fraction of Ti atoms titrated by PPA was strongly dependent on synthesis method and surface density. PPA titration and benzyl alcohol photooxidation may be useful measures of surface accessibility in other supported oxides.
AB - It can be difficult to determine the number of active atoms accessible to the fluid phase in mixed oxide catalysts, as required for obtaining true turnover frequencies (TOF). Here, we utilize the selective titration of surface Ti atoms with phenylphosphonic acid (PPA) on TiO2-SiO2 materials to estimate the number of reactant-accessible sites. TiO 2-SiO2 composites were synthesized over a range of Ti loadings from grafting of titanocene dichloride (Cp2TiCl2) or tetraethoxy orthotitanate (TEOT) on SiO2 and sol-gel co-hydrolysis of Si and Ti alkoxides. The materials were characterized by DRUV-vis, XRD, BET, and XANES. Despite the significant morphological and electronic differences, materials prepared by Cp2TiCl2 and TEOT yielded a near-constant TOF of 0.14 h-1 (±0.04) across Ti loadings, for benzyl alcohol photooxidation, when normalizing rates by sites titrated by PPA. The fraction of Ti atoms titrated by PPA was strongly dependent on synthesis method and surface density. PPA titration and benzyl alcohol photooxidation may be useful measures of surface accessibility in other supported oxides.
KW - Active site
KW - Photocatalysis
KW - Supported oxide
KW - Titania
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U2 - 10.1016/j.jcat.2013.09.015
DO - 10.1016/j.jcat.2013.09.015
M3 - Article
AN - SCOPUS:84886004547
VL - 309
SP - 156
EP - 165
JO - Journal of Catalysis
JF - Journal of Catalysis
SN - 0021-9517
ER -