Selective Photocatalytic Conversion of Methane Induced by Lewis Acid–Base Pair on the Surface of In<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> Heterojunction Photocatalyst
Yanmei Chen, Sishi Tang, Li Li, Xingman Liu, Jun Liang
Abstract
The efficient catalytic conversion of light-driven methane (CH 4 ) is still very challenging. Here, the surface-reconstructed In 2 O 3 /TiO 2 heterojunction photocatalyst is successfully prepared by a two-step operation of ion exchange and calcination, and the efficient selective photocatalytic conversion of CH 4 is achieved. In the absence of O 2, the formation rates of ethane (C 2 H 6 ) and hydrogen (H 2 ) are 68.9 and 78.6 μmol h –1 g –1, respectively, which corresponds to the stoichiometric ratio. However, in the presence of O 2 or water (H 2 O) as the oxidant, CH 4 is converted to CO, and the CO formation rates are 113.2 and 94.4 μmol h –1 g –1, respectively. Our results show that the In 3 –O 2– Lewis acid–base pair on the In 2 O 3 /TiO 2 surface can realize the adsorption and activation of CH 4 . Moreover, the photogenerated hole-induced reactive oxygen centers (Ti 4+ O ·– Ti 4+ OH – and Ti 4+ O 2– Ti 4+ O ·– ) on the surface of In 2 O 3 /TiO 2 are identified as the active species for inducing the dissociation of CH 4 into ·CH 3 radicals, which in turn are coupled into C 2 H 6 by ·CH 3 . In contrast, in the presence of O 2, the surface superoxide anion (O 2 – ), surface ·O – radicals, and O 2 2– anions are identified as the active species for inducing the oxidation of CH 4 into CO.