Enhanced hydroisomerization of n-heptane over bifunctional catalysts with highly dispersed Pd nanoparticles supported on H-Yβ composite zeolite

Enhanced catalytic hydroisomerization efficiency and iso-alkanes selectivity by exploring the bifunctional zeolite-supported metal catalysts at the nanoscale are of great important in petrochemical and coal chemical industries. Herein, we develop a simple two-step strategy for introducing intracrystalline and intercrystalline mesopores in H-Yβ by in-situ compositing and loading Pd nanoparticles (NPs, ∼2.2 nm) through an incipient wetness impregnation process followed by mild oxidation–reduction treatment. Especially, the Pd@H-Yβ catalyst with synergistic acid sites and highly dispersed Pd NPs inherits the large surface area, high crystallinity and graded mesoporous channels, and strong thermal and hydrothermal stability. As a demonstration, Pd@H-Yβ with extremely low Pd NPs loading amount of 0.2 wt% used for catalytic hydroisomerization of n-heptane (n-C7) by cascade dehydrogenation and hydrogenation on Pd NPs and isomerization on accessible acid sites, and exhibits an extraordinarily yield of i-heptane (i-C7,74.7 %) compared to the conventional Pd@H-Y (49.1 %) and Pd@H-β (33.7 %) at 280 °C for 3 h under 1 MPa initial hydrogen pressure (IHP). Furthermore, first-principle calculations reveal that the high catalytic activity of Pd@H-Yβ originates from the active hydrogen (H…H and/or H+) transfer by the facile H2 dissociation. The diffusion limitations of intermediates and secondary cracking reactions are effectively weakened due to intrinsic mesoporous channels in Pd@H-Yβ, which still maintains high catalytic activity after 5 times recycles. These findings provide a rational design strategy of bifunctional catalysts with adjustable metal–acid active sites for low-molecular reactants hydroisomerization in industrial application.