Tuning the Surface Alloy Composition of Phosphorus-Promoted Ni–Co Bimetallic Nanoparticles for Selective Tandem Hydrogenation

Selective tandem hydrogenation is a promising strategy for catalytic conversion of bulk raw materials with multifunctional groups into high-value-added chemicals via multiple-step reactions. Yet now, one of the current challenges is to develop a multifunctional and stable catalyst enabling the tandem catalysis rather than interrupting at any step reaction, particularly for supported nonprecious metal catalysts. In this work, we report tandem hydrogenation of bulk phthalic anhydride toward the one-pot synthesis of hexahydrophthalide, an emerging monomer of a recyclable polyester, over phosphorus-promoted Ni–Co bimetallic alloy nanoparticle catalysts. The surface composition of catalysts can be easily regulated by changing the Ni/Co molar ratio and the phosphorous functionalization strategy, which could then tune the product selectivity and enhance the stability of this tandem process. The optimal Ni3Co1@NC-P affords 88% selectivity for the desired product and demonstrates promising stability toward the tandem hydrogenation reaction. Systematic experimental and computational studies reveal that the adsorption strength of the intermediates and the ability of hydrogen activation can be altered by the formation of surface metallic Ni species, thus tuning the product selectivity. In addition, the oxidation resistance of Ni3Co1@NC-P was enhanced by the phosphorization treatment, which makes the bimetallic alloy successfully realize the tandem hydrogenation reaction. The finding of this work not only provides a convenient strategy to design and develop efficient and stable non-noble metal-based catalysts for selective tandem hydrogenation reactions, especially involving the hydrodeoxygenation reaction, but also fulfills the straightforward pathway for the preparation of degradable polyester monomer hexahydrophthalide.