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Metal-specific reactivity in single-atom-catalysts: CO oxidation on 4d and 5d transition metals atomically dispersed on MgO

DOI: 10.1021/jacs.0c03627 DOI Help

Authors: Bidyut B. Sarma (Max-Planck-Institut für Kohlenforschung) , Philipp N. Plessow (Karlsruhe Institute of Technology) , Giovanni Agostini (ALBA Synchrotron Light Source) , Patricia Concepcion (Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas (UPV-CSIC)) , Norbert Pfänder (Max-Planck-Institut für chemische Energiekonversion) , Liqun Kang (University College London (UCL)) , Feng R. Wang (University College London) , Felix Studt (Karlsruhe Institute of Technology) , Gonzalo Prieto (Max-Planck-Institut für Kohlenforschung; Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas (UPV-CSIC))
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society

State: Published (Approved)
Published: August 2020
Diamond Proposal Number(s): 17377 , 19072

Abstract: Understanding and tuning the catalytic properties of metals atomically dispersed on oxides are major stepping-stones towards a rational development of single-atom catalysts (SACs). Beyond individual showcase studies, the design and synthesis of structurally regular series of SACs opens the door to systematic experimental investigations of performance as a function of metal identity. Herein, a series of single-atom catalysts based on various 4d (Ru, Rh, Pd) and 5d (Ir, Pt) transition metals has been synthesized on a common MgO carrier. Complementary experimental (X-ray absorption spectroscopy) and theoretical (Density Functional Theory) studies reveal that, regardless of the metal identity, metal cations occupy preferably octahedral coordination MgO lattice positions under step-edges, hence highly confined by the oxide support. Upon exposure to O2-lean CO oxidation conditions, FTIR spectroscopy indicates the partial de-confinement of the monoatomic metal centers driven by CO at pre-catalysis temperatures, followed by the development of surface carbonate species under steady-state conditions. These findings are supported by DFT calculations, which show the driving force and final structure for the surface metal protrusion to be metal-dependent, but point to an equivalent octahedral-coordinated M4+ carbonate species as the resting state in all cases. Experimentally, apparent reaction activation energies in the range of 96±19 kJ/mol are determined, with Pt leading to the lowest energy barrier. The results indicate that, for monoatomic sites in SACs, differences in CO oxidation reactivity enforceable via metal selection are of lower magnitude than those evidenced previously through the mechanistic involvement of adjacent redox centers on the oxide carrier, suggesting that tuning of the oxide surface chemistry is as relevant as the selection of the supported metal.

Journal Keywords: Single-atom catalysts; coordination confinement; XAS spectroscopy; In situ CO-FTIR; CO oxidation

Subject Areas: Chemistry

Instruments: B18-Core EXAFS

Other Facilities: ALBA