Synthesis And Catalytic Hydrogenation Properties Of Core-Shell Structure Nanomaterials

Heterogeneous catalytic hydrogenation process plays an important role in the chemical industry and has a significant impact on social development.In order to achieve ideal catalytic hydrogenation performance,people have been committed to developing catalysts with high activity,high selectivity and long-term stability under reaction conditions for a long time.For different types of heterogeneous catalytic hydrogenation reactions,the component modification and fabrication of core-shell structure often exhibit different properties.Therefore,according to the features of different reactions and the modification mechanism of core-shell structure,in this paper,metal nanoparticles with different composition and structure as the core,by using large specific surface area of MOFs,CeO₂ and carbon nitrogen materials coating and loading,improve the catalytic performance of metal nanoparticles.A series of core-shell materials with different composition and structure of metal nanoparticles have been successfully designed and synthesized.The activity,selectivity and stability of core-shell nanomaterials were regulated by controlling their composition and structure.The main achievements are as follows:1.We report an in-situ method for construction of a core-shell structured Pt-Ni1.6 NF@Ni-MOF-74.This is attributed to the Ni-MOF-74 shell in situ formed in the preparation process,which can stabilize the evolved Pt-Ni NF and donate electrons to the Pt metals that facilitate the preferential adsorption of electrophilic-NO₂ group.Therefore,the sample exhibits not only 100%conversion for the selective hydrogenation of 4-nitrostyrene to 4-aminostyrene conducted at room temperature,but also good selectivity（92%）and high stability（no activity loss after fifteen runs）during the reaction.2.In order to achieve controlled synthesis of core-shell nanomaterial structures,we report the design and fabrication of a high-performance tandem catalyst（CeO₂/Pt/NC/Co）by preciously manipulating the landing place of Co species in the hierarchical CeO₂/Pt/N doped C（NC）nanoreactor via a facile wet-chemistry route.The inner Co nanoparticles play an essential role of an activity regulator by denoting their electrons to neighboring Pt nanoparticles.Meanwhile,the outer Co nanoclusters play a crucial role of a selectivity regulator by altering the adsorption configuration of benzylideneaniline intermediates.Benefiting from the unique“dual-regulator effect”,a remarkably-improved catalytic efficiency（100%nitrobenzene conversion with 94%N-benzylaniline selectivity）is achieved in the hydrogenation of nitrobenzene and benzaldehyde catalyzed by CeO₂/Pt/NC/Co at a relatively low temperature of 80℃。3.In order to improve the simplicity of synthesis of core-shell nanomaterials,we fabricate a novel copper-cerium mixed metal oxide（CuO_x-CeO₂）via a controllable surface deposition route.The results indicate the significance of the interactions between CuO_x and CeO₂,which can facilitate the activations of H₂ and CO₂ simultaneously,so that promote the formation of formates intermediates.CuO_x-CeO₂ exhibits the highest catalytic activity with approximately 31%CO₂ conversion and 98%CO selectivity at 380℃,as well as excellent stability for 50 h.4.In order to further study core-shell nanomaterials with more complex compositions based on the third work,we fabricate CuO_x-Pd@CeO₂ nanomaterials via chemical replacement and nanoparticle deposition.The deposition of CeO₂ nanoparticles lead to the enrichment of electron density on Pd,which is conducive to H₂ dissociation.In the process of CuO_x-3Pd@CeO₂ catalytic hydrogenation of phenylacetylene,the H atom activated by Pd can overflow onto the Cu base for hydrogenation of phenylacetylene to styrene.The interface of Cu2O and Pd is stabilized by phenylacetylene,which reduces the adsorption of styrene and improves the selectivity of styrene.Therefore,CuO_x-3Pd@CeO₂ shows higher phenylacetylene conversion and styrene selectivity under atmospheric pressure of 50℃ hydrogen atmosphere.