Abstract
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.
| Original language | English |
|---|---|
| Pages (from-to) | 156-165 |
| Number of pages | 10 |
| Journal | Journal of Catalysis |
| Volume | 309 |
| DOIs | |
| Publication status | Published - 2014 |
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Keywords
- Active site
- Photocatalysis
- Supported oxide
- Titania
ASJC Scopus subject areas
- Catalysis
- Physical and Theoretical Chemistry
Cite this
Quantifying accessible sites and reactivity on titania-silica (photo)catalysts : Refining TOF calculations. / Eaton, Todd R.; Campos, Michael P.; Gray, Kimberly A.; Notestein, Justin M.
In: Journal of Catalysis, Vol. 309, 2014, p. 156-165.Research output: Contribution to journal › Article
}
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
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
UR - http://www.scopus.com/inward/record.url?scp=84886004547&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84886004547&partnerID=8YFLogxK
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 -