Spatially Structured Materials

摘要

Zeolites with uniform microporous structures have been widely used in heterogeneous catalysis. To optimize their utilization, their primary particles should be no larger than a few tenths of nanometers, as in this case the diffusion path is relatively short while preserving the beneficial properties of the zeolite, i.e. selectivity and high specific surface area. But such small zeolite particles can not be directly used in industry due to high pressure drop, and they are normally mixed with clays and extruded into beads or pellets (1). The clay offers physical ruggedness under reaction conditions, but it hinders mass transport of reactants into and products out of the zeolite catalyst. Fortunately, recently developed amorphous mesoporous materials are excellent media to support such nano-sized zeolites, due to their large pores, for instance, SBA-15 and TUD-l with tunable pores up to about 25-30 nm, (2, 3) thus overcoming the mass-transport barrier imposed by clay binders. So a composite with nano-sized zeolite homogeneously incorpo- rated into a three-dimensional mesoporous material would be an ideal class of catalytic materials.