Synergistic La2O3-La(OH)3 interface engineering enables deep and durable dehydrogenation of 12H-N-propylcarbazole over Pd/Al2O3 catalysts

Abstract

Targeting the demand for efficient dehydrogenation catalysts in liquid organic hydrogen carriers, we synthesized a series of La-doped alumina supports by a co-precipitation/hydrothermal route and deposited Pd nanoparticles to promote 12H-N-propylcarbazole (NPCZ) dehydrogenation. Comprehensive characterization shows that an optimal 10 wt % La loading generates intimately interfaced La₂O₃ and La(OH)₃ nanodomains that anchor highly dispersed Pd particles (∼2.2 nm), donate electrons to Pd⁰, and create bifunctional acid-base sites together with a fast hydrogen-spillover network. These synergistic features accelerate C–H activation and H-migration, enabling Pd/La₁₀AlO to deliver the theoretical H₂ release (5.43 wt %) in 150 min at 180 °C with 99% NPCZ selectivity and no activity loss over ten cycles. Kinetic analysis reveals markedly lower apparent activation energies for all three successive dehydrogenation steps, with a ∼65 kJ·mol⁻¹ drop in the rate-limiting 4H-NPCZ→NPCZ stage, underscoring the thermodynamic and kinetic benefits conferred by the dual-phase La promoter. This work provides the first mechanistic evidence that coexisting La₂O₃/La(OH)₃ can cooperatively tune the electronic and interfacial structure of Pd/Al₂O₃, offering clear guidelines for designing durable, high-performance dehydrogenation catalysts for N-heterocyclic liquid organic hydrogen carriers.