Theoretical Study On The Structure And Catalytic Mechanism Of Non-noble Metal Superatom Clusters

As a special kind of atomic cluster,the superatom can mimic the physical and chemical properties of atoms in the periodic table.Its advantage lies in the substitution of scarce or expensive elements,which lays a foundation for the construction of three-dimensional periodic table.In recent decades,theoretical and experimental researchers have explored and perfected the principles of the electronic construction of superatoms,designed different properties of superatomic clusters,and applied them to the construction of new electronic,optical,magnetic and mechanical properties of nanostructured materials.At the same time,the catalytic properties of the superatom clusters have been studied,which not only provide the possibility for regulating the chemical behavior of the materials and improving their chemical applications,but also have important applications in the design and synthesis of energy storage and energy conversion materials.In this paper,the cheap metal clusters were taken as the research object,and non-noble metal supratom clusters(Zro)n-/0(n=1-5)and Al12Mg were designed using different design rules based on the density functional theory(DFT),and the micro reaction mechanism for the splitting reaction of H2O and the CO oxidation reaction were systematically studied,respectively.The major achievements and innovations are as follows:(1)Although the non-noble ZrO cluster can be used as a superatom to replace the noble metal Pd,the geometric/electronic structures and chemical bonding of larger ZrO-polymeric clusters are unclear.Herein,by using density functional theory(DFT)calculations,the lowest-energy structures of the(ZrO)n-/0(n=2-5)clusters were optimized,in which every O atom in these clusters tends to connect its adjacent two Zr atoms forming metal oxygen bridge bonds.Insights into the electronic characteristics of these clusters were obtained by analyzing their molecular orbitals(MOs)and density of states(DOS).More importantly,the complexes formed by the connection of Zr3O3 cluster with different ligands CO(electron acceptor)and PH3(electron donor)and Zr3O3 cluster under the oriented external electronic field(OEEF)were studied,unveiling that the ligand field and OEEF can greatly alter the electronic characteristics of clusters by tuning the HOMO and LUMO states to form superalkali metal clusters and superhalogens.Strikingly,the successive attachment of PH3 on Zr3O3 dramatically lowers the adiabatic ionization potential(AIP)of the ligated clusters,resulting in the formation of stable superalkali clusters with large HOMO-LUMO gaps;the increment of the OEEF results in the remarkable enhancement of the electron affinity(EA)of Zr3O3,which turns it into superhalogen.Furthermore,the potential of constructing the superalkali Zr3O3(PH3)5 based 1-D cluster assembled material was also examined.(2)DFT calculations were employed to study H2O dissociation with(ZrO)n and Pdn clusters,both clusters have isocovalent electrons.The findings revealed that the primary reaction processes and molecular orbitals(MOs)of clusters are similiar.The course of reactions is to activate one H2O molecule through cluster catalysis,via an intermediate step of H transfer to the metal,followed by H-H recombination and H2 desorption from clusters to produce H2,ZrnOn+1 and PdnO.The latter of which can react with one CO molecule to regenerate(ZrO)n and Pdn.Therefore,a fully catalytic cycle for H2O dissociation by CO mediated with the clusters can be proposed.Nevertheless,a clear difference is observed from the exothermic reaction of(ZrO)n and endothermic reactions of Pdn with water,indicating the non-noble metal superatomic clusters not only maintain the similarity of the reaction mechanism of noble metal clusters,but also show the superiority of kinetics in the catalytic reaction.(3)Because the CO oxidation is a crucial reaction in many important industrial processes,it is of great significance to search for cheap and efficient catalysts and understand their micro reaction mechanism.According to the density functional theory(DFT).we calculate the structure and electronic properties of Al12Mg,Al12MgLin(n=1-5)and Al12Mg2 clusters.The former features large EA and HOMO-LUMO gap with a 1S21 P61D102S21F142P4 valence electronic structure,which not only show its stability but indicate analogous to a chalcogen atom as a superchalcogens cluster.Meanwhile,the latter Al12MgLi2 and Al12Mg2 shows the ionic property with a forty-electron(40e)closed-shell jellium model electronic configuration.What's more,for the investigation of the CO oxidation mechanism with Al12Mg,Al12MgLi,Al12MgLi2 and Al12Mg2,the full pathways and transition states for the reactions have been identified,which reflect Al12MgLi2 is more reactive in CO oxidation reaction than others,identifying the adsorption sites,smaller EA and charging effect play important roles in CO oxidation reaction.Here,the studies of superatom Al12Mg and its compounds enrich the fundamental knowledge on Al,Mg,Li-based clusters,which are conducive to the future experimental characterization and catalytic application.