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

Nishiguchi, H Zhang, JL Anpo, M Masuhara, H

H. Nishiguchi et al., Photochemical properties of benzophenone adsorbed on Ti-Al binary oxides: The effects of the surface acidity, J PHYS CH B, 105(16), 2001, pp. 3218-3222

28

INGLESE

Article

Physical Chemistry/Chemical Physics

JOURNAL OF PHYSICAL CHEMISTRY B

1520-6106 → ACNP

105

16

2001

3218 - 3222

ISI

1520-6106(20010426)105:16<3218:PPOBAO>2.0.ZU;2-5

Ti-Al binary oxides prepared by a coprecipitation method exhibit different chemical behaviors from those of physically mixed TiO2-Al2O3 oxides, and th e dispersion of the TiO2 species in the Ti-Al binary oxides increases when the composition of Al of the starting materials is increased. When benzophe none is adsorbed on the Ti-Al binary oxides, the photochemical and photophy sical properties of benzophenone are found to be greatly different from tho se of benzophenone adsorbed on porous silica glass such as Vycor glass. Nam ely, the phosphorescence properties of benzophenone adsorbed on Ti-Al binar y oxides show the presence of the protonated form of benzophenone in additi on to the benzophenone hydrogen-bonded to the surface OH groups. The charac teristics of the surface properties, structures, and activities of these bi nary oxides are examined by monitoring the characteristics of the isomeriza tion of cis-2-butene as a probe reaction. The phosphorescence properties of the protonated and hydrogen-bonded form of benzophenone changed with varia tions in the Ti/Al ratio, exhibiting a good correspondence with the results of the cis-2-butene to l-butene and cis to trans isomerization reactions o f cis-2-butene on the Ti-Al binary oxides, respectively. These good relatio nships suggest that the double bond shift isomerization reaction of cis-2-b utene to l-butene and the geometrical cis to trans isomerization occur at d ifferent sites, that is, the active sites for the cis-2-butene to l-butene isomerization may be the surface Bronsted acid sites and the active sites f or cis to trans isomerization may be the surface OH groups located on Al2O3 . Direct detection of the transient absorption spectra of benzophenone adso rbed on the oxides indicates that the benzophenone ketyl radicals are forme d on the surfaces of Al2O3 through the hydrogen abstraction from the acidic surface OH groups by the excited triplet state of benzophenone.