Hollow Hierarchical Silicalite-1 Zeolite Encapsulated PtNi Bimetals for Selective Hydroconversion of Methyl Stearate into Aviation Fuel Range Alkanes

Hollow hierarchical silicalite-1 zeolite encapsulated Pt and PtNi bimetals (Pt@HS-1 and PtNi@HS-1) were successfully synthesized via a ship-in-bottle strategy and employed for hydroconversion of methyl stearate into aviation fuel range alkanes in a fixed-bed reactor. Their morphologies, texture, and acidity were characterized by field-emission scanning electron microscopy, field-emission transmission electron microscopy, X-ray diffraction, nitrogen adsorption and desorption, hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectrometry, ammonia temperature-programmed desorption, and CO pulse chemisorption. The bimetallic catalysts (PtNi/S-1 and PtNi@HS-1) showed higher catalytic activity and selectivity to aviation fuel owing to the stronger cleavage ability related to the introduction of Ni species. Moreover, aviation fuel selectivity was significantly improved on the hollow hierarchical encapsulated catalysts than their precursors, ascribed to the extended contact time between reactants and active sites. A maximum aviation fuel selectivity of 45% was obtained for the PtNi@HS-1 catalyst at 360 °C under 3 MPa. Furthermore, the PtNi@HS-1 catalyst exhibited superior catalytic stability and selectivity than the PtNi/S-1 catalyst during the stability test. This indicates that the hollow hierarchical encapsulated structure plays crucial roles in enhancing aviation fuel selectivity and catalytic performance.