  Metal oxides have been extensively investigated and applied in environmental
remediation and protection, energy conversion and storage. Most of these
diverse applications are results of a large diversity of the electronic states
of metal oxides. Noticeably, however, numerous metal oxides have obstacles for
applications in catalysis because of low density of active sites in these
materials. Size reduction of oxide catalyst is a strategy to improve the active
site density. Here, we demonstrate the fabrication of single atomic metal oxide
in which the oxide size reaches its minimum. However, the catalytic mechanism
in this SATO is determined by a quasi atom physics which is fundamentally
distinct from the traditional size effect, and also is in contrast to the
standard condensed matter physics. SATO results in a record high and stable
sunlight photocatalytic degradation rate of 0.24, which exceeds those of
available photocatalysis by approximately two orders of magnitude. The
photocatalytic process is enabled by a quasi atom physical mechanism, in which,
an electron in the spin up channel is excited from HOMO to LUMO+1 state, which
can only occur in SATO with W5+.
