Design,Synthesis And Catalytic Application Of Yolk-shell Nanoreactors With Multi-metal Cores

Traditional supported nanocatalysts have been widely used in modern industrial catalysis production,which have the characteristics of simple synthesis method and fast mass transfer.However,after long-term use,the metal nanoparticles as the active component will reduce the catalytic activity due to sintering,that is,the stability is poor.To solve that,the concept of core-shell nanoreactors has been proposed to improve the stability of catalysts by encapsulating active components with inert material shells.Among them,the yolk-shell structure nanoreactor has attracted the attention of the majority of scientific researchers because of its unique hollow structure.Its shell can not only effectively prevent the loss of active components,so that the catalyst has excellent stability,the cavity can also increase the collision probability between reactant molecules and active components through the void-confinement effect,thereby improving the catalytic activity.However,due to the limitation of synthesis methods,the composition of active component nanoparticles in yolk-shell nanoreactors is often relatively simple,and it is difficult to obtain better catalytic performance.In this paper,the inverse microemulsion&hard template-assisted synthesis strategy was used.The active component precursors are first wrapped in SiO₂ nano-microspheres in the inverse microemulsion system,and then used as a hard template to prepare a ZrO₂ or phenol formaldehyde resin organic carbon film on the SiO₂ surface by using n-butyl alcohol zirconium hydrolysis or resorcinol formaldehyde condensation.After calcination and removing SiO₂ by alkali etching,a variety of functionalized active nanoparticles were successfully encapsulated in porous ZrO₂ or microporous carbon hollow shell and the Au-Fe₂O₃@ZrO₂,Rh Cu@HCS,Pt Pd Ni@HCS,and PtPdSnCoNi@HCS nanoreactors with yolk-shell structures were synthesized.After the microstructure and the state of active component nanoparticles were determined by TEM,XPS,XRD,bet and other characterizations,the nanoreactors were applied to a variety of heterogeneous catalytic reactions,and their catalytic properties were tested.Compared with the Au@ZrO₂ nanoreactor with the same structure,the strong metal-support interaction of dumbbell-shaped Au-Fe₂O₃ nanoparticles significantly improved the CO oxidation activity of Au in the yolk-shell Au-Fe₂O₃@ZrO₂nanoreactor;Compared with the Au-Fe₂O₃/ZrO₂ supported catalyst,the void-confinement effect also improves the catalytic activity.Moreover,due to the protective effect of the ZrO₂ shell,the Au-Fe₂O₃@ZrO₂ nanoreactor has superior high temperature stability,the hollow structure and CO oxidation catalytic activity did not change after being calcined in an air atmosphere at 900°C.After introducing Cu into Rh to form alloy nanoparticles in yolk-shell Rh Cu@HCS nanoreactor,although a part of the hydrogenation activity of halogenated nitrobenzene is reduced,the selectivity of halogenated aniline was significantly improved through the interaction between Rh and Cu.Since the Rh Cu alloy nanoparticles are encapsulated inside the HCS cavity,the catalytic activity and selectivity of the Rh Cu@HCS nanoreactor remain unchanged after 8 cycles in the hydrogenation of p-chloronitrobenzene.The yolk-shell structure Pt Pd Ni@HCS nanoreactor is used in the hydrogenation of styrene.Compared with the nano reactor of HCS encapsulated single metal or bimetallic alloy nanoparticles,the Pt Pd Ni ternary alloy is due to the interaction between the three metal elements,showing extremely high hydrogenation activity.Under the reaction conditions of room temperature,atmospheric pressure and 1wt%catalyst dosage,the conversion rate of styrene can reach nearly 100%in only 45 minutes,and it is widely applicable to olefin-based substrates.In addition,the excellent catalytic stability is also reflected in the catalyst recycling.Based on the above synthesis experience,a new synthesis method of high-entropy alloy nanoparticles was proposed,that is,SiO₂ nanospheres wrapped with five metal composite hydroxide clusters were synthesized by inverse microemulsion.The SiO₂shell plays a physical confinement role,and five metal elements are confined inside the silicon spheres for reduction to form high-entropy alloy nanoparticles.Using this as a hard template,a yolk-shell structure PtPdSnCoNi@HCS nanoreactor was synthesized for the first time.Although the content of each metal element is similar macroscopically,it is found that some PtPdSnCoNi high-entropy alloy nanoparticles have uneven distribution and phase separation of Sn and Co by EDS-mapping characterization,which belong to gradient high-entropy alloy.This part of the work provides new ideas for the synthesis and structural design of high-entropy alloy-based catalysts.The synthetic strategy involved in this paper is not limited to the synthesis of the above-mentioned yolk-shell structured nanoreactors,but can also be extended to the synthesis of yolk-shell structured nanoreactors encapsulating other complex active nanoparticles for application in more diverse heterogeneous catalytic reactions.