Figure 2: Schematic of synthesis of a catalyst of singly dispersed bimetallic sites M1An.
(a) Well-crystallized reducible oxide substrate, AxOy. (b) Deposition of hydroxide species of guest metal, M(OH)z, to surface of the oxide support, AxOy; a low concentration of M cations (0. 5 wt% or less) allows them to be singly dispersed on the surface of AxOy; the atomic ratio of M atoms to A atoms of the topmost layer of atoms A of AxOy is typically <5–10%; M(OH)z species are weakly bound to the surface of AxOy. (c) Formation of singly dispersed M1On species upon oxidation in 5% O2 at 150 °C; M cations are bonded to AxOy surface through M–O–A bonds. (d) A controlled reduction in 5% H2; removal of oxygen atoms between M and A atoms by reduction in H2 makes M directly bond with A atoms of oxide support, forming an M1An site; as M atoms are singly dispersed on AxOy (due to the low concentration of guest atoms M), the formed M1An bimetallic sites are isolated. They are called singly dispersed bimetallic sites.
