Photochemical properties of benzophenone adsorbed on Ti-Al binary oxides: The effects of the surface acidity

H. Nishiguchi, J. L. Zhang, M. Anpo*, Hiroshi Masuhara

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

Ti-Al binary oxides prepared by a coprecipitation method exhibit different chemical behaviors from those of physically mixed TiO2-Al2O3 oxides, and the dispersion of the TiO2 species in the Ti-Al binary oxides increases when the composition of Al of the starting materials is increased. When benzophenone is adsorbed on the Ti-Al binary oxides, the photochemical and photophysical properties of benzophenone are found to be greatly different from those of benzophenone adsorbed on porous silica glass such as Vycor glass. Namely, the phosphorescence properties of benzophenone adsorbed on Ti-Al binary oxides show the presence of the protonated form of benzophenone in addition to the benzophenone hydrogen-bonded to the surface OH groups. The characteristics of the surface properties, structures, and activities of these binary oxides are examined by monitoring the characteristics of the isomerization of cis-2-butene as a probe reaction. The phosphorescence properties of the protonated and hydrogen-bonded form of benzophenone changed with variations in the Ti/Al ratio, exhibiting a good correspondence with the results of the cis-2-butene to 1-butene and cis to trans isomerization reactions of cis-2-butene on the Ti-Al binary oxides, respectively. These good relationships suggest that the double bond shift isomerization reaction of cis-2-butene to 1-butene and the geometrical cis to trans isomerization occur at different sites, that is, the active sites for the cis-2-butene to 1-butene isomerization may be the surface Brönsted acid sites and the active sites for cis to trans isomerization may be the surface OH groups located on Al2O3. Direct detection of the transient absorption spectra of benzophenone adsorbed on the oxides indicates that the benzophenone ketyl radicals are formed on the surfaces of Al2O3 through the hydrogen abstraction from the acidic surface OH groups by the excited triplet state of benzophenone.

Original languageEnglish
Pages (from-to)3218-3222
Number of pages5
JournalJournal of Physical Chemistry B
Volume105
Issue number16
DOIs
StatePublished - 26 Apr 2001

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