Confinement effects of carbon nanotubes in catalytic energy conversion processes

Carbon materials have properties different from conventional oxides in catalysis, in particular as catalyst supports. Recently, carbon nanotubes (CNTs) attract attention with their well defined tubular morphology and their electron structure in the graphene walls, where π electrons shift from the inside to the outside due to the curvature. This provides an intriguing confinement environment for nanocatalysts and catalytic reactions inside such small cavities. Using Fe as a probe, it is found that the redox properties of iron oxide and metallic iron are modified when they are confined inside the CNT channels with respect to those dispersed on the outer surface of CNTs. As a result, its activity for Fischer-Tropsch synthesis is obviously enhanced benefiting from formation of more catalytically active iron carbides under reaction conditions. Similarly, a significant enhancement of the catalytic activity of Rh particles confined inside nanotubes for the conversion of syngas to C2 oxygenates has also been observed compared to the outside catalyst although the latter is much better accessible to reactants. The confinement effects of CNTs in other catalytic energy conversion processes are also reported recently.Carbon materials have properties different from conventional oxides in catalysis, in particular as catalyst supports. Recently, carbon nanotubes (CNTs) attract attention with their well defined tubular morphology and their electron structure in the graphene walls, where π electrons shift from the inside to the outside due to the curvature. This provides an intriguing confinement environment for nanocatalysts and catalytic reactions inside such small cavities. Using Fe as a probe, it is found that the redox properties of iron oxide and metallic iron are modified when they are confined inside the CNT channels with respect to those dispersed on the outer surface of CNTs. As a result, its activity for Fischer-Tropsch synthesis is obviously enhanced benefiting from formation of more catalytically active iron carbides under reaction conditions. Similarly, a significant enhancement of the catalytic activity of Rh particles confined inside nanotubes for the conversion of syngas to C2 oxygenates has also been observed compared to the outside catalyst although the latter is much better accessible to reactants. The confinement effects of CNTs in other catalytic energy conversion processes are also reported recently