Hierarchically meso -macroporous metal

It is found that hierarchically meso/macroporous metal oxides can be synthesized even without the use of any external macrotemplate. In fact, great efforts have been made by scientists to promote development of hierarchically porous materials via the spontaneous self-formation phenomenon from metal alkoxides during the past decade. In this section, we will review the history of self-formation phenomenon to target hierarchically porous materials based on metal alkoxides. 

Meso-Macroporous Mixed Oxides Multicomponent oxides play a central role in chemical and petrochemical processing as catalysts and as supports for catalytically active species [145]. It is known that the catalytic efficiency of metal oxides can be improved by doping them with a metal or combining them with another metal oxide [145]. The strategy based on the self-formation phenomenon to fabricate the porous hierarchy demonstrated its simplicity and superiority in the synthesis of hierarchically meso-macroporous metal oxides with multiple compositions. 

Nb-based catalysts are among the investigated systems in total removal of -butanol due to the capacity of niobium to adopt variable oxidation states. Thus, Nb-doped hierarchically micro(meso) macroporous Ti02 (anatase phase) (Figure 17.10) synthesized via a self-formation procedure showed close performances with catalysts in which the same materials served as supports for noble metals [46]. The efficiency of these catalytic systems in the total oxidation of butan-l-ol was enhanced by the improved diffusion through the intrinsic macro-porous network. An effect of the niobium content was evidenced as welL... 

Besides the biomaterials mentioned above, the cuttlebone [49] and chito-san [50] with unique structure have also been used as templates for the formation of hierarchically porous materials, which maintained the biological structure. Starch gel and dextran were also used to produce hierarchically sponge-like micro-, meso/macroporous monoliths of silicalite and meso/macro-porous metal oxides [51,52]. 

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