RTI uses cookies to offer you the best experience online. By clicking “accept” on this website, you opt in and you agree to the use of cookies. If you would like to know more about how RTI uses cookies and how to manage them please view our Privacy Policy here. You can “opt out” or change your mind by visiting: http://optout.aboutads.info/. Click “accept” to agree.
Counting active sites on titanium oxide-silica catalysts for hydrogen peroxide activation through in situ poisoning with phenylphosphonic acid
Eaton, T. R., Boston, A. M., Thompson, A. B., Gray, K. A., & Notestein, J. M. (2014). Counting active sites on titanium oxide-silica catalysts for hydrogen peroxide activation through in situ poisoning with phenylphosphonic acid. ChemCatChem, 6(11), 3215-3222. https://doi.org/10.1002/cctc.201402611
Quantifying specific active sites in supported catalysts improves our understanding and assists in rational design. Supported oxides can undergo significant structural changes as surface densities increase from site-isolated cations to mono-layers and crystallites, which changes the number of kinetically relevant sites. Herein, TiOx domains are titrated on TiOx-SiO2 selectively with phenylphosphonic acid (PPA). An ex situ method quantifies all fluid-accessible TiOx, whereas an in situ titration during cis-cyclooctene epoxidation provides previously unavailable values for the number of tetrahedral Ti sites on which H2O2 activation occurs. We use this method to determine the active site densities of 22 different catalysts with different synthesis methods, loadings, and characteristic spectra and find a single intrinsic turnover frequency for cis-cyclooctene epoxidation of (40+/-7) h(-1). This simple method gives molecular-level insight into catalyst structure that is otherwise hidden when bulk techniques are used.