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EPR Studies of Photoreduction of Ni/TiO 2 Catalysts
Author(s) -
Chien ShuHua,
Wei YuWen,
Lin MauChen
Publication year - 1997
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.199700031
Subject(s) - electron paramagnetic resonance , chemistry , nickel , catalysis , ion , rutile , inorganic chemistry , hydrogen , photochemistry , paramagnetism , analytical chemistry (journal) , nuclear magnetic resonance , physics , organic chemistry , biochemistry , quantum mechanics , chromatography
Irradiations of Ni/TiO 2 catalyst by UV in hydrogen at 77 K produced not only Ni + ions on the catalyst surface, but also Ni 3+ and Ti 3+ species in bulk or near the interface between nickel and titania. These photo‐generated species were detected and characterized by low temperature electron paramagnetic resonance (EPR) spectroscopy. Relative spin concentrations of the photogenerated paramagnetic species (Ni n+ and Ti 3+ ) varied with the nickel content in titania. A high nickel content in the sample resulted in a high peak intensity ratio of Ni n+ to Ti 3+ . It was found that the photoinduced self‐redox reaction of Ni 2+ ions to form Ni + and Ni 3+ ions has a priority over the photoreduction of Ti 4+ to Ti 3+ ions. The characteristic EPR spectrum of the Ni 3+ (3d 7 ) ions with g 1 = 2.268, g 2 = 2.237, and g 3 = 2.045 indicates that the Ni 3+ ions are most likely located in the substitutional sites of TiO 2 , possibly near the surface rutile phase. The Ni + species (3d 9 ) with g 4 = 2.130 and g 1 = 2.063 are on the surface of TiO 2 . Both Ni + and Ni 3+ ions are quite stable in hydrogen. The Ni 3+ ions seem to be responsible for anchoring the nickel ions onto titania and stablizing the Ni + species on the surface. The Ni + ions are thus free from oxygen poisoning and still show a high activity toward olefin oligomerization.