Reductive amination of furfuryl alcohol, furfural and 5‐hydroxymethylfurfural (5‐HMF) were carried out on various metal catalysts. Over Raney Ni catalyst, we obtained the highest furfurylamine yields of 81.8 % and 94.0 % from furfuryl alcohol in absence and presence of H2, respectively. While furfural was used as the substrate, 100 % yield of furfurylamine could be achieved over Raney Ni under rather moderate conditions. Although 5‐HMF was completely converted over all catalysts used, the highest yield of 2,5‐bisaminomethylfuran (60.7 %) was obtained over Raney Ni at 160 °C in 12 h. The DFT calculations on the adsorption behavior of NH3 and H2 on different metal surfaces showed that the difference of the adsorption energy between NH3 and H2 on Ni is lower than those of other metals, indicating that less metal active sites on Ni surface is occupied by NH3, which leaves more active sites for dehydrogenation/hydrogenation reactions and in the end promotes the reductive amination reactions.
Simultaneous reductive amination of C=O and C−OH in 5‐hydroxymethylfurfural (HMF) into C−NH2 in 2,5‐bis(aminomethyl)furan (BAMF) is challenging. In this work, reductive amination of C=O in HMF was firstly studied, in which HMF can be converted into 5‐hydroxymethyl furfurylamine (HMFA) with a 99.5 % yield over Raney Co catalyst. BAMF was then directly synthesized with 82.3 % yield from HMF over Raney Ni catalyst at 160 °C for 12 h. An even higher yield of 88.3 % could be obtained through a stepwise reductive amination process, in which the reaction started at 120 °C for the first 2 h over Raney Co mainly for amination of C=O and then continued at 160 °C for another 10 h over Raney Ni mainly for amination of C−OH. Under optimized reaction conditions, the catalyst could be reused four times without obvious loss in catalytic performance. XRD and XPS characterization of the reused catalyst indicated that the formation of Ni3N and the adsorption of alkyl amines could be the main reasons for the deactivation of the catalyst. Moreover, plausible reaction pathways were proposed to originate the detected by‐products according to the kinetic profiles.
Switchable reductive amination of furfuryl alcohol to tetrahydrofurfurylamine and furfurylamine was realized by adding/not adding H2 over a RANEY® Ni catalyst.
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