title: Revealing the Size-Dependent d-d Excitations of Cobalt Nanoparticles Using Soft X-ray Spectroscopy.
abstract: Cobalt-based catalysts are widely used to produce liquid fuels through the Fischer-Tropsch (FT) reaction. However, the cobalt nanocatalysts can exhibit intriguing size-dependent activity whose origin remains heavily debated. To shed light on this issue, the electronic structures of cobalt nanoparticles with size ranging from 4 to 10 nm are studied using soft X-ray absorption (XAS) and resonant inelastic X-ray scattering (RIXS) spectroscopies. The RIXS measurements reveal the significant size-dependent d-d excitations, from which we determine that the crystal-field splitting energy 10Dq changes from 0.6 to 0.9 eV when the particle size is reduced from 10 to 4 nm. The finding that larger Co nanoparticles have smaller 10Dq value is further confirmed by the Co L-edge RIXS simulations with atomic multiplet code. Our RIXS results demonstrate a stronger Co-O bond in smaller Co nanoparticles, which brings in further insight into their size-dependent catalytic performance.
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale and Department of Materials Science and Engineering, University of Science and Technology of China , Hefei 230026, Anhui, China.|Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China , Hefei 230026, Anhui, China.
authors.forename: Zhangzhang
authors.initials: Z
authors.lastname: Cui
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.
authors.forename: Chenlu
authors.initials: C
authors.lastname: Xie
authors.affiliation: State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Science , Shanghai 200050, China.
authors.forename: Xuefei
authors.initials: X
authors.lastname: Feng
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.
authors.forename: Nigel
authors.identifier: http://orcid.org/0000-0001-7857-6841
authors.initials: N
authors.lastname: Becknell
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Peidong
authors.initials: P
authors.lastname: Yang
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale and Department of Materials Science and Engineering, University of Science and Technology of China , Hefei 230026, Anhui, China.|Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China , Hefei 230026, Anhui, China.|National Synchrotron Radiation Laboratory, University of Science and Technology of China , Hefei 230026, Anhui, China.
authors.forename: Yalin
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale and Department of Materials Science and Engineering, University of Science and Technology of China , Hefei 230026, Anhui, China.|Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China , Hefei 230026, Anhui, China.
authors.forename: Xiaofang
authors.initials: X
authors.lastname: Zhai
authors.affiliation: State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Science , Shanghai 200050, China.
authors.forename: Xiaosong
authors.initials: X
authors.lastname: Liu
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Wanli
authors.initials: W
authors.lastname: Yang
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Yi-De
authors.initials: YD
authors.lastname: Chuang
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Department of Chemistry and Biochemistry, University of California , Santa Cruz, California 95064, United States.
authors.forename: Jinghua
authors.identifier: http://orcid.org/0000-0002-8576-2172
authors.initials: J
authors.lastname: Guo