Controllable Preparation Of Metal-acid Site Synergistic Catalysts By LDHs Precursor Method For Reductive Amination

Biomass resources are expected to provide sustainable energy and fine chemicals as a substitute for fossil raw materials due to their renewable and wide-ranging advantages.Amine compounds have a wide range of applications in pharmaceutical,agricultural,and biodegradable fields,but most of them are currently derived from fossil resources.Therefore,the research on reductive amination of biomass platform molecules can provide a new and greener way for the synthesis of amine compounds.Furfural is a typical biomass platform molecule,and its reductive amination to efficiently obtain the target product furfurylamine is very challenging,which not only includes the main reaction of amination and reduction in sequence,but also the coupling side reaction of reactants and intermediates and the competitive hydrogenation reaction.It has been reported in the literature that Ru-based catalysts perform well in reductive amination reactions,but the scarcity and high price of precious metals limit their wide applications.In recent years,non-precious metal catalysts represented by Ni and Co have also been reported,but these catalysts require harsh reaction conditions and are difficult to meet the needs of selective control in complex reactions,and there is still much room for improvement in catalytic performance.Alloying with the second metal component to optimize the geometry and electronic structure of the metal active center is a common method for improving the performance of single-metal catalysts.Therefore,designing a synergistic catalyst of non-noble bimetallic and acidic support is expected to realize the efficient synthesis of furfurylamine.Layered double hydroxides（LDHs）are typical two-dimensional layered materials,and the electronic effect generated by their lattice structure is conducive to the co-reduction of bimetallic components to induce the formation of alloy structures,resulting in abundant surface Lewis acid sites.Based on this background,this thesis aims to improve the selectivity of primary amines in the reductive amination reaction of furfural.The synergistic construction of catalyst alloy structures and acid bifunctional sites was achieved by utilizing the tunable denaturation of chemical composition and structure of LDHs.Therefore,a series of Ni-based non-precious metal catalysts were synthesized,revealing the synergistic mechanism of Ni Co alloy and acid sites of Ni Co/Ni Co Al O_xcatalysts in the reductive amination of furfural,and further elucidating the effect of alloy electronic structure on furfurylamine selectivity.（1）Taking the reductive amination enhancement of furfural as the starting point,Ni Co/Ni Co Al O_x alloy/acid bifunctional was prepared by in situ reduction method based on the structural topology effect of Ni Co Al-LDHs,Ni Mg Al-LDHs and Co Mg Al-LDHs as precursors catalyst.Combined with HAADF-STEM and H₂-TPR characterization find that Ni and Co form an alloy structure,and the electronic interaction between Ni and reducible Co further promote the reduction of Co²⁺to Co⁰,and it can be significantly optimized when n_（Ni）/n_（Co）=3 alloy structure.The performance evaluation results show that the Ni Co/Ni Co Al O_x catalyst achieved 100%conversion and 95.0%furfuryl amine selectivity under mild reaction conditions,while Ni/Ni Mg Al O_x only achieve 77.0%furfuryl amine selectivity under the same conditions.H₂-TPD characterization and in situ IR experiments reveal that the Ni Co alloy not only promotes the activation and dissociation of H₂ molecules,but the alloy is a favorable site for Schiff base C=N bond adsorption in（C&N）type.In addition,NH₃-TPD combined with IR prove that the strong acid site can effectively improve the activation and dissociation ability of the catalyst for NH₃.Under the synergistic effect of the dominant alloy sites and strong acid sites,it ensures that the Schiff base can be converted into furfuryl amine by amination and hydrogenation,avoiding it direct hydrogenation to generate secondary amine,which leads to the improvement of catalyst performance.（2）In order to further explore the influence of the electronic effect of the alloy catalyst on the selectivity of furfurylamine,a series of Ni Fe/Ni Fe Al O_x,Ni Co/Ni Co Al O_x,Ni Cu/Ni Cu Al O_x and Ni Ga/Ni Ga Al O_xalloys were prepared by in-situ topological reduction based on LDHs precursors with different compositions.H₂-TPR,XRD,HRTEM and other characterizations confirm the successful construction of the alloy structure,VB（XPS）further reveals that the bonding energy corresponding to the center of the alloy d-band is different.Py-IR studies show that the above catalyst supports have similar acid strengths,realizing the precise control of Ni-based alloys and acid sites by layered precursor method.When the furfural conversion rate of the four catalysts is 100%,the order of selectivity to furfuralamine is:Ni Fe/Ni Fe Al O_x（96.1%）>Ni Co/Ni Co Al O_x（95.0%）>Ni Ga/Ni Ga Al O_x（82.0%）>Ni Cu/Ni Cu Al O_x（64.4%）,in which the selectivity order is linearly negatively correlated with the binding energy of the alloy d-band central.Through the infrared desorption experiment of the product furfurylamine,it is found that the change of the d-band center affects the desorption of the product furfurylamine on the alloy surface,thereby improving the selectivity of the furfurylamine formation.