Regulating Encapsulation of Small Pt Nanoparticles inside Silicalite-1 Zeolite with the Aid of Sodium Ions for Enhancing n-Hexane Reforming

Metal dispersion and the stability of metal-based catalysts are critical for improving the catalytic performance of a reforming reaction to produce aromatics. In this work, with the aid of Na +, well-dispersed and highly stable Pt nanoparticles encapsulated in silicalite-1(Sil-1) zeolite to form Pt@Sil-1- x Na catalysts with different amounts of Na + were prepared with a simple one-pot hydrothermal method and applied in the reforming of n -hexane to aromatics. For comparison, both Pt@Sil-1 without Na and Pt/Sil-1 by traditional incipient wetness impregnation were also prepared and investigated for the reaction. The catalytic results reveal that the Pt@Sil-1- x Na catalysts could exhibit better catalytic performance for n -hexane reforming than that of the Pt/Sil-1 catalyst. The Pt@Sil-1-4Na catalyst with the proper amount of Na + gave a full conversion of 100% with a high benzene selectivity of 76.8% for n -hexane reforming at 500 °C and had excellent operating stability during a period of 120 h. The characterization of the as-synthesized different catalysts by various techniques reveals that both the encapsulation structure of Sil-1 and the presence of Na + can reduce the size of Pt nanoparticles and enhance the interaction between Pt nanoparticles and the Sil-1 zeolite, thus improving both the activity and stability of the catalyst. Moreover, the addition of Na + can also regulate the acidity/basicity of Sil-1 zeolite, which is in favor of suppressing some side reactions such as cracking, isomerization, etc., thus increasing the selectivity of aromatics. A possible mechanism for n -hexane reforming over the Pt@Sil- x Na catalysts is proposed.