Preparation Of Single-atom Catalysts And Their Organic Catalytic Reaction Applications

The increasing demand for sustainable energy and the sustainable development of the environment have become the focus of scientists all over the world.Atomic level dispersed single atom catalysts have attracted increasing attention due to their excellent catalytic activity,high selectivity and almost 100%atomic utilization.In many fields,such as environmental energy and biomedicine,etc.,it is of great significance to find a heterogeneous single atoms catalyst with high efficiency,low cost and high selectivity.The single atom catalysts can be used as an ideal bridging model between heterogeneous and homogeneous catalysis.In addition,the catalytic performance of single atom catalysts are highly correlated with their exact coordination structure,monodisperse state and supports.Different supports materials,such as nitrogen-doped carbon,defect-enriched metal oxides/sulfides/carbides,have been reported to be used as matrixes to load individual metal atoms.In practical industrial catalytic applications,over 80%of the reactions require supported heterogeneous catalysts for product transformation.Studies have shown that when the size of metal catalysts decrease from nanometer scale to subnanometer scale and finally to the limit size of single atom,single atoms catalysts usually exhibit different catalytic properties to nanoparticles.In addition,single atoms catalysts greatly exposed atomic sites and increased site density.Coordination unsaturated environment,quantum size effect and enhanced metal-supports interaction synergistic boost the intrinsic activity of single atom catalysts.In addition,single atom catalysts have high specific surface energy,and it is easy for conventional synthesis methods to cause atomic agglomeration.Based on this,the purpose of this paper is to explore a reasonable and controllable single atom catalysts preparation strategy,and to explore the catalytic performance of single atom catalyst,mainly including the following aspects:1.Two-step carbothermal welding to access atomically dispersed Pd1 on three-dimensional zirconia nanonet.We selected the amino modified UiO-66-NH2 MOF as the object,and used its three-dimensional channels to restrict the subject palladium chloride molecule,so as to achieve the role of the confined palladium chloride molecule.The uncoordinated free-NH2 on the 2-amino-terephthalic acid ligand in UiO-66-NH2 was used as Lewis base to stabilize the noble metal divalent Pd2+ion.The strong interaction between the lone pair electrons in the amino group and the d-orbital of the precious metal limits a single Pd ion to the pore of the three-dimensional porous MOF.Through the domain limiting effect of UiO-66-NH2 on Pd ions,the agglomeration of Pd atoms can be effectively prevented in the high temperature carbonization process,thus forming monodispersed palladium atomic sites.Two types of palladium monoatoms can be obtained by two-step carbonization,which is anchored to nitrogen-doped carbon and three-dimensional porous zirconia carrier obtained by node fusion.The monatomic catalyst synthesized by us was used directly to test the indoles synthesis catalysis.The Pd monatomic atom with Pd-O coordination has obviously superior performance than that of Pd-N/C coordination,which is of great significance for the preparation of monatomic catalysts.2.Atomically dispersed Ru catalyst prepared by hydrothermal migration for highly efficient hydrodeoxygenationWe reported for the first time a new kind of solid phase strategy induced by ammonia migration,this method can directly strip Ru single atoms from bulk Ru sponge and then under hydrothermal conditions embedding in the amorphous microtubules supports(Ru1@m-tube).The process greatly simplifies the synthesis route and reduces the cost,the actual use is of great significance for industrial production.During the catalyst preparation process,first,NH3 generated by the hydrolysis of melamine can pull the surface Ru atoms from Ru sponge to form water-soluble Ru(NH3)x.Then,melamine and hydrolysates(cyanuric acid)were assembled into a scoped melamine-cyanuric acid(MCA)supramolecular micron rod by in-situ polymerization,and Ru(NH3)x was restricted to the MCA matrix(Ru(NH3)x@m-rod).Finally,the NH3 molecules is removed from Ru(NH3)x@m-rod at high temperature to produce a dense surface binding Ru1 site(Ru1@m-tube).This process leads to hollow microstructure and a large number of surface defects,which may help capture and enrich these migrating Ru species.Ru1@m-tube can be used as a durable semi-homogeneous catalyst to enhance the hydrodeoxygenation of 4-hydroxy-3-methoxybenzaldehyde at 393 K with excellent TOF(1301.4h-1)and 96.4%selectivity.