The study provides
deep insight into the origin of photocatalytic
deactivation of Nb
2
O
5
after modification with
ceria. Of particular interest was to fully understand the role of
ceria species in diminishing the photocatalytic performance of CeO
2
/Nb
2
O
5
heterostructures. For this purpose,
ceria was loaded on niobia surfaces by wet impregnation. The as-prepared
materials were characterized by powder X-ray diffraction, nitrogen
physisorption, UV–visible spectroscopy, X-ray photoelectron
spectroscopy, high-resolution transmission electron microscopy, and
photoluminescence measurements. Photocatalytic activity of parent
metal oxides (i.e., Nb
2
O
5
and CeO
2
) and as-prepared CeO
2
/Nb
2
O
5
heterostructures
with different ceria loadings were tested in methanol photooxidation,
a model gas-phase reaction. Deep insight into the photocatalytic process
provided by
operando
-IR techniques combined with
results of photoluminescence studies revealed that deactivation of
CeO
2
/Nb
2
O
5
heterostructures resulted
from increased recombination of photo-excited electrons and holes.
The main factor contributing to more efficient recombination of the
charge carriers in the heterostructures was the ultrafine size of
the ceria species. The presence of such highly dispersed ceria species
on the niobia surface provided a strong interface between these two
semiconductors, enabling efficient charge transfer from Nb
2
O
5
to CeO
2
. However, the ceria species supported
on niobia exhibited a high defect site concentration, which acted
as highly active recombination centers for the photo-induced charge
carriers.