Pore size-tunable core-shell structured Ni-Ru Nanoparticles catalyst for the reductive amination of isosorbide diketone

Abstract

Isosorbide has been produced on a large scale and is expected to become the most important raw material for producing diaminoisomannide (DAIS) as a monomer for synthesis of polyamides. However, the direct catalytic amination of isosorbide to DAIS is impossible over heterogeneous catalysts, therefore, a two-step process, consisting of oxidation of isosorbide to isosorbide-diketone (ISDK) and reductive amination of ISDK to DAIS, has been proposed. The second step is key to realize this process. Therefore, a series of core-shell structured Ni-Ru nanoparticles bimetallic catalysts (Ni-Ru@SiO2 and meso-Ni-Ru@SiO2) for the reductive amination of ISDK to DAIS have been developed by doping ruthenium to Ni@SiO2. Among the catalysts, the meso-Ni-Ru@SiO2 catalyst (Ni: Ru = 76, Si: Ni = 0.625, C18TMS: Si = 0.2) demonstrated the highest catalytic activity in the catalytic amination of ISDK to DAIS, and the yield of DAIS reached up to 99 % with a turnover frequency (TOF) of 26.90 s−1. The catalyst also showed excellent performance in the catalytic amination of various aldehydes and ketones including (hetro)aromatic aldehydes and ketones as well as aliphatic aldehydes and ketones. The characterization results revealed that the Ni-Ru nanoparticles in the catalyst are uniformly dispersed and encapsulated within the SiO2 shell, and the doped Ru can adjust the electronic state of Ni. The porosity and pore size of the SiO2 shell can be tuned by adjusting the amount of C18TMS during the formation of the SiO2 shell, which facilitate the performance of the catalyst. Density functional theory (DFT) calculation in combination with experimental validation have shown that the porosity and pore size of the SiO2 shell affect the diffusion efficiency of reactants and products.