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, 10 (1), 4998

Quasi Pd 1 Ni Single-Atom Surface Alloy Catalyst Enables Hydrogenation of Nitriles to Secondary Amines

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Quasi Pd 1 Ni Single-Atom Surface Alloy Catalyst Enables Hydrogenation of Nitriles to Secondary Amines

Hengwei Wang et al. Nat Commun.

Abstract

Hydrogenation of nitriles represents as an atom-economic route to synthesize amines, crucial building blocks in fine chemicals. However, high redox potentials of nitriles render this approach to produce a mixture of amines, imines and low-value hydrogenolysis byproducts in general. Here we show that quasi atomic-dispersion of Pd within the outermost layer of Ni nanoparticles to form a Pd1Ni single-atom surface alloy structure maximizes the Pd utilization and breaks the strong metal-selectivity relations in benzonitrile hydrogenation, by prompting the yield of dibenzylamine drastically from ∼5 to 97% under mild conditions (80 °C; 0.6 MPa), and boosting an activity to about eight and four times higher than Pd and Pt standard catalysts, respectively. More importantly, the undesired carcinogenic toluene by-product is completely prohibited, rendering its practical applications, especially in pharmaceutical industry. Such strategy can be extended to a broad scope of nitriles with high yields of secondary amines under mild conditions.

Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Synthesis and morphologies of xPd-Ni/SiO2 bimetallic catalysts. a Schematic illustration of synthesis of xPd-Ni/SiO2 bimetallic catalysts using selective Pd ALD. b Pd loadings in the xPd-Ni/SiO2 and xPd/SiO2 samples determined by ICP-AES. c STEM image of 20Pd-Ni/SiO2 and the corresponding EDS elemental mapping signals: Ni Kα (d), Pd Lα (e) and the constructed Ni + Pd (f). Scale bar in c 20 nm. g A representative HAADF-STEM image of 5Pd-Ni/SiO2. Isolated Pd single atoms on partially-oxidized Ni NPs were highlighted by brown arrows. Scale bar: 2 nm. h Intensity profile along the line X–Y in g highlighting the presence of Pd single atoms. i A representative HAADF-STEM image of 20Pd-Ni/SiO2. Scale bar: 2 nm. The red circles in i highlight contrast of the inner core and outer shell of the NPs. j A STEM image of 20Pd-Ni/SiO2. k EDS line profile analysis across the NP in j
Fig. 2
Fig. 2
Catalytic performances of Pd/SiO2, Pt/SiO2, and 5Pd-Ni/SiO2 catalysts in hydrogenation of BN and hydrogenolysis of BA. Time profiles of hydrogenation of BN over Pd/SiO2 (a), Pt/SiO2 (b) and 5Pd-Ni/SiO2 (c), and their corresponding TOFs (d). Reaction conditions: solvent, ethanol, 60 mL; BN, 0.5 g; catalyst, 30 mg; H2 pressure, 0.6 MPa; temperature, 80 °C. e Recyclability test of the 5Pd-Ni/SiO2 sample. Reaction conditions: solvent, ethanol, 60 mL; BN, 1 g; catalyst, 100 mg; H2 pressure, 0.6 MPa; temperature, 80 °C; reaction time, 2 h. The larger amount of substrate and catalyst here is only for a purpose of the convenience of recycling. f Time profiles of hydrogenolysis of BA over Pd/SiO2, Pt/SiO2 and 5Pd-Ni/SiO2. Reaction conditions: solvent, ethanol, 60 mL; BA, 0.5 g; catalyst, 30 mg; H2 pressure, 0.6 MPa; temperature, 80 °C
Fig. 3
Fig. 3
Structural characterization of xPd-Ni/SiO2 bimetallic catalysts. a In situ Fourier transforms EXAFS spectra of the xPd-Ni/SiO2 samples (x = 5, 10, and 20) and Pd foil reference in the real space at the Pd K-edge. A model of core-shell like Pd1Ni SASA structure for 5Pd-Ni/SiO2 is illustrated as the inset in a, where the dark blue and light blue balls are Pd and Ni atom, respectively. b DRIFTS CO chemisorption of the xPd-Ni/SiO2 samples (x = 5, 10, and 20) at the CO saturation coverage. The dark blue, gray, and red balls in b are Pd, C, and O atom, respectively. Scale bar: 0.01. c In situ XPS spectra of xPd-Ni/SiO2 samples (x = 5, 10, and 20) and a Pd/SiO2 reference in the Pd 3d region
Fig. 4
Fig. 4
The reaction paths of hydrogenation of BN on metal surfaces. a Reaction pathways of hydrogenation of BN. b Energy profiles of the key intermediates and transition states involved in a on Pd(111), Pt(111), and Pd1@Ni(111) surfaces. The energy barriers of the consecutive hydrogenation and hydrogenolysis steps are highlighted by the yellow squires. The Pd, Pt, Ni, C, N, and H atoms are shown in green, violet, light blue, gray, blue, and white, respectively. On the right side of b, the product distribution over the corresponding metal surfaces was highlighted, where the thicker the arrows represents the higher selectivity
Fig. 5
Fig. 5
Catalytic performance of 5Pd-Ni/SiO2 catalyst in hydrogenation of substituted nitriles. Reaction conditions: nitrile, 0.5 g; ethanol, 60 mL; catalyst, 30 mg; temperature, 80 °C; H2, 0.6 MPa. 0.25 g nitrile, 65 °C. 0.125 g nitrile, 65 °C

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