One-step synthesis of H-β zeolite-enwrapped Co/Al₂O₃ Fischer-Tropsch catalyst with high spatial selectivity

A tailor-made encapsulated catalyst with a H-β zeolite shell has been directly synthesized over Co/Al₂O₃ pellets to form a core-shell structure without pinholes and cracks by a hydrothermal synthesis method. Pretreatment of the Co/Al₂O₃ pellets with reflux of hot TEAOH solution can clean and corrode the pellet surface due to its strong basicity, and can enlarge the mean pore size of the pellets. Impregnation of the Co/Al₂O₃ pellets in EtOH is important to avoid the corrosion of the internal pores, to prevent the introduction of Co species into the zeolite coating, and to realize a pure and uniformed β-zeolite coating. For the catalytic reaction of direct isoparaffin synthesis from syngas, the molar ratio of C_isoparaffin/C_{normal-paraffin} of the products obtained from the encapsulated catalyst increased about 64% than that of the products obtained from physical-mixed components. This concept of encapsulated catalyst can be useful to carry out various consecutive or multiple-step catalytic processes, where multiple reactions occur on different active centers.