Pd/NiO/Al Array Catalyst for 2-Ethylanthraquinone Hydrogenation: Synergistic Effect Between Pd and NiO/Al Support

Abstract

Manipulating the surface acidic/basic property and pore structure of support are two effective approaches to increase catalytic performance of Pd-based catalyst in anthraquinone (eAQ) hydrogenation. Herein, to combine two promoting approaches, array-typed NiO/Al supported Pd catalyst were synthesized. By regulating preparation method, three Ni(OH)₂/Al support precursors showed different morphologies of nest-like, face-to-face packed and dandelion-like structure, respectively. After loading Pd, three Pd/NiO/Al catalysts exhibited different catalytic performance in eAQ hydrogenation, among which the nest-like catalyst possessed the highest H₂O₂ space time yield of 107.5 g g_Pd⁻¹ h⁻¹ with > 99% selectivity to active anthraquinone. Detailed characterizations were performed to investigate the pore structure, basic property and electronic structure caused by different morphologies of catalysts, to explain the structure-performance relationship. Specifically, on the basis of ensuring effective collision of reactant molecules, the outer opening pores (20–100 nm) could decrease diffusion barriers of eAQ/eAQH₂, which improves active site accessibility for eAQ and benefits desorption of eAQH₂. In addition, suitable amount of weak basic sites Ni²⁺–OH with high electronic density appropriately improves surface electronic density of Pd NPs, which moderately enhances H₂ activation/dissociation but could not lead to over hydrogenation to give deeply hydrogenated byproducts.

Graphical Abstract