Hierarchical, core–shell meso-ZSM-5@mesoporous aluminosilicate-supported Pt nanoparticles for bifunctional hydrocracking

Abstract

A series of well-defined, core–shell-structured composite materials comprising microporous/mesoporous ZSM-5 as core and mesoporous aluminosilicate as shell were synthesized by combining controlled desilication using sodium hydroxide solution with subsequent self-assembly using a triblock copolymer. An aluminosilicate shell with uniform mesopores was grown closely around the crystals of mesoporous ZSM-5, with a tunable thickness of 60–300 nm, by adjusting the extent of desilication. The obtained composite zeolites exhibited a hierarchical porosity containing the original regular MFI micropores (ca. 0.56 nm) and desilication-induced, randomly distributed mesopores (5–50 nm), both within the core ZSM-5 crystals, as well as relatively uniform mesopores (ca. 6 nm) inside the shell part on the zeolite surface. The mesoporous aluminosilicate shell, self-assembled from the MFI zeolite fragments as a result of partially dissolved ZSM-5 crystals, demonstrated weak acidity and much higher hydrothermal stability in comparison to the shell synthesized by the additional silica source. Taking advantage of the confining effect of the mesopores, Pt nanoparticles were incorporated into the mesoporous shells, giving rise to bifunctional catalysts, which exhibited a higher selectivity of C₅–C₁₁ liquid products compared to the conventional Pt/ZSM-5 catalyst in the hydrocracking of n-hexadecane.