Hierarchical hollow zeolite fiber in catalytic applications: A critical review.

Zeolites have widely been studied because of the better performance as catalysts and supports. However, the zeolites with only micropores have drawbacks in reactivity and selectivity due to limitation of diffusivity. The hollow zeolite fibers (HZF) with hierarchical porosity however can overcome the problem. The HZF can be synthesized by such methods as incorporated substrate removal method, solid-solid transformation method, co-axial electrospinning technology, dry-wet spinning technology, and hollow fiber incorporation method. The unique hierarchical porous structure leads to the great improvement in the diffusion efficiency of reactants. The catalytic zeolite membrane fibers are the most commonly used as they have stronger catalyst stability and higher catalytic selectivity. The HZFs are suitable in catalytic applications such as selective catalysis, CO preferential oxidation, air purification and wastewater treatment. In order that the HZFs can be applied to industrial operations, more research work should be carried out, such as developments of self-assembly pure HZFs, catalytic substrate incorporated HZFs, HZFs with gradient multicomponent zeolites and HZFs with nanoscale diameters.