DFT Study on the Support Effect of Supported Metal Catalyst and Reactivity

Author:Gu Yong Bing

Supervisor:wang jian guo zhuang gui lin

Database:Doctor

Degree Year:2019

Download:23

Pages:103

Size:5446K

Keyword:

Supported metal catalysts based on carbon materials,metal oxides,molecular sieves etc.are widely used in chemical,pharmaceutical,energy and other industries.With the further study,It has been found that supports not only support metal particles,but also regulate the dispersion of metal particles and change the electronic structure of metals through the interaction between supports and metals,so as to achieve high activity and stability of catalysts.some supports even participate in the activation process and have synergistic effects with metals,and become an indispensable part of catalysts.Based on the density functional theory(DFT)calculations,revealing the relationship between the structure and performance of catalysts and understanding the support effect and interface effect of supported catalysts are of great significance for the design and synthesis of supported metal catalysts with excellent performance.In this work,graphyne and C2N with special nanopore are used as supports to study the configuration and electronic property of suppored transition metals,and the effects of graphyne and C2N nanopore on atomic dispersion of transition metals and reactivity are investigated.By establishing a reversed-phase supported catalyst model,the support effect of noble metal supported by oxides is studied,and the mechanism of the synergistic effect between supports and metals on the high activity of catalysts is revealed.The main findings are as follows:1.Aiming at the problem that the weak interaction between carbon support and metal leads to the agglomeration of supported metal particles,the effect of graphyne with natural nanopore on controlling and reactivity of supported Pd single atoms is studied based on DFT theory.The strong interaction between graphyne and Pd results from the chelating coordination of acetylene group to Pd,which promotes the dispersion and stability of Pd single atoms in graphyne nanopore.The reactivity of Pd@graphyne is studied using CO as a model reaction and the interaction between reactant and supported metal can stimulate the reactivity of the catalyst.2.Based on DFT calculations,the support effect on the supporting and reactivity of the first transition series metals on graphyne is studied.Geometric factor affects the structures of TM@graphyne.The regular change of cohesive energy reflects the interaction of graphyne with different transition metals.The strong interaction between graphyne and transition metals changes the electronic structure of transition metals,and affects the adsorption of small molecules such as CO and O2.The oxidation of CO on Fe@garphyne undergoes a bimolecular adsorption mechanism with a maximum reaction energy barrier of 0.59 eV.The strong interaction between graphyne and Fe weakens the adsorption of O,and the reaction energy barrier for further reaction of O with CO to produce CO2 is cut down to 0.18 eV.3.Using the supported reversed-phase Al2O3/Au(111)as model cataylst,the support and interface effect on supported Au catalyzed CO oxidation is investigated by DFT calculations.O2 is not prefer to adsorbed on Au(111)clean surface because that Au is not a good electron donor.In the presence of Al2O3,the empty orbital of highly oxidized Al may disperse the bonding electrons of O2,which is beneficial to the electron transfer from Au to the antibonding orbital of O2.The synergistic effect between oxide and gold is the intrinsic reason that O2 can be adsorbed and highly activated at the interface site.The CO oxidation reaction at the interface of Al2O3/Au(111)experiences an association mechanism.The participation of CO is helpful for the dissociation of O2 with an intermediate of COO2 formed.The maximum Gibbs free energy barrier of 0.15 eV in association mechanism explained perfectly the excellent CO oxidation activity of supported Au at very low temperature.4.Using the two-dimensional N-containing material C2N as support,the effect of C2N on transiton metal supporting and N2 reduction reaction(NRR)on TM@C2N is studied by DFT calculations.The strong interaction between support and transition metal comes from the chelation of N in C2N to transition metal.Transition metal atoms are embedded into the nanopore and transfer electrons to the support.The adsorption of N2 and its hydrogenation intermediates on TM@C2N is regulated by strong C2N-TM interaction.NRR reaction on V@C2N and Mo@C2N has low theoretical overpotential through enzymatic pathway.The DFT studies in this paper reveales the nature of support effect based on strong support-metal interaction or support-metal synergy,provides theoretical explanation at atomic and molecular levels for support-controlled reactivity of catalyst,and provides theoretical basis and guidance for the experimental preparation of supported metal catalysts and single-atom catalysts(SACs)with high activity and stability.