**2.3 Re+7 oxides**

The bulk rhenium regarding its inorganic chemistry that possesses +7 oxidation states is slightly sparse. Numerous ortho-rhenate compounds covering isolated units of ReO4 which are somewhat common: KReO4, NaReO4, and NH4ReO4. Bulk Re2O7 holds a layered structure comprising of interchanging groups of ReO4 and ReO6, along with subunits of rings that are constituted two groups of both ReO4 and ReO6. The weak bonding among rhenium oxide groups in the layered structure of Re2O7 consequences in the effective vaporization of Re2O7 dimers that hold two groups of ReO4 bridged through one O atom for example gaseous O3Re–O–ReO3. The supreme possible surface ReOx attention on oxide supports is permanently reduced than monolayer attention due to the surface ReOx species association to produce volatile dimers (Re2O7) at extreme surface coverage. Moreover, crystalline Re2O7 is not ever perceived as this MO is not stable to higher calcination values along with the introduction to ambient moisture. Therefore, mono-layer ReOx with its surface coverage is not ever gotten because crystalline Re2O7 and volatilization does certainly not exist. Hence, supported ReOx catalysts are exceptional between the sustained MO catalysts. In this materialization, only surface ReOx attention below single-layer can be accomplished deprived of the occurrence of crystallites [15, 28, 29].
