CO2 and Water Activation on Ceria Nanocluster Modified TiO2 Rutile (110)
2018-02-02T13:20:24Z (GMT)
by
Surface modification of TiO<sub>2</sub> with metal oxide nanoclusters is
a strategy for the development of new photocatalyst materials. We have studied modification
of the (110) surface of rutile TiO<sub>2</sub> with ceria nanoclusters using
density functional theory corrected for on-site Coulomb interactions (DFT+U).
We focus on the impact of surface modification on key properties governing the
performance of photocatalysts, including light absorption, photoexcited charge
carrier separation, reducibility and surface reactivity. Our results show that
adsorption of the CeO<sub>2</sub> nanoclusters, with compositions Ce<sub>5</sub>O<sub>10</sub>
and Ce<sub>6</sub>O<sub>12</sub>, is favourable at the rutile (110) surface and
that the nanocluster-surface composites favour non-stoichiometry in the
adsorbed ceria so that reduced Ce ions will be present in the ground state. The
presence of reduced Ce ions and low coordinated O sites in the nanocluster lead
to the emergence of energy states in the energy gap of the TiO<sub>2</sub>
host, which potentially enhance the visible light response. We show, through an
examination of oxygen vacancy formation, that the composite systems are
reducible with moderate energy costs. Photoexcited electrons and holes localize
on Ce and O sites of the supported nanoclusters. The interaction of CO<sub>2</sub>
and H<sub>2</sub>O is favourable at multiple sites of the reduced CeO<sub>x</sub>-TiO<sub>2</sub>
composite surfaces. CO<sub>2</sub> adsorbs and activates, while H<sub>2</sub>O
spontaneously dissociates at oxygen vacancy sites.
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