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TYC Highlight Seminar: Unraveling the nature of single-atom catalysts

Gianfranco Pacchioni

Dipartimento di Scienza dei Materiali, Università Milano-Bicocca, via R. Cozzi, 55, I-20125, Italy

Thursday 23 April 2020
Time: 4pm
Venue: UCL Physics A1/3, followed by a reception in the Nyholm Room, Christopher Ingold Building, Gordon Street
Contact: Karen Stoneham
Tel: 0207 679 7306

Abstract

Single-atom catalysis is a new frontier in heterogeneous catalysis due to the high activity and selectivity for various catalytic reactions, from CO oxidation to cellulosic biomass conversion, from  water–gas shift to methanol and ethanol dehydrogenation, etc. [1,2]. In the past, single-atom catalysts could not be clearly visualized and characterized due to limitations associated with instrument resolution. In the last years, however, the development of new characterization techniques, high-resolution scanning transmission electron microscopy (STEM), extended X-ray absorption fine structure (EXAFS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), etc. have permitted to identify the presence of single-atoms on active catalysts. Still, many open questions remain about these materials: (a) the nature of the atomic species (charged, neutral, etc.), (b) the sites where they are stabilized, and how these sites can prevent aggregation, (c) the role of the support, (d) the dynamic behavior depending on reaction conditions, etc. In this talk we discuss the nature of isolated Rh, Ru and Pt species deposited on two representative oxide surfaces, anatase TiO2 (a reducible oxide), and tetragonal ZrO2 (a non-reducible oxide) [3-7]. These systems have been characterized experimentally using STEM, FTIR and temperature programmed desorption (TPD) spectra of adsorbed CO probe molecules [3-7]. Combining these data with extensive Density Functional Theory (DFT) calculations we provide an unambiguous identification of the stable single-atom species present on these supports. Single metal atoms assume different configurations depending on the treatment of the catalyst. The isolated metal species can adopt a range of local coordination environments and oxidation states, which evolve in response to varied environmental conditions [5]. In all cases considered the observed species consist of metal atoms bound to surface hydroxyl groups (M-OH), or to one (M-O) or two (M-O2) oxygen atoms on the surface arising from the interaction of the deposited metal with surface OH groups [Mads + OHads ® (M-O)ads + ½H2(g)]. Thus, surface hydroxyl (OH) groups play a key role in providing a solid anchor for metal atoms on oxide supports, explaining their high thermal stability.

 

[1] A. Wang, J. Li, T. Zhang, “Heterogeneous single-atom catalysis”. Nature Reviews Chemistry, 2, 65-81, (2018).

[2] X. F. Yang, A. Wang, B. Qiao, J. Li, J. Liu, T. Zhang, “Single-atom catalysts: a new frontier in heterogeneous catalysis”. Accounts of chemical research, 46, 1740-1748, (2013).

[3] H. V. Thang, G. Pacchioni, L. De Rita, P. Christopher, “Nature of stable single atom Pt catalysts dispersed on anatase TiO2”, J. of Catalysis, 367, 104-114 (2018).

[4] H. V. Thang, S. Tosoni, L. Fang, P. Bruijnincx, G. Pacchioni, “Nature of sintering-resistant, single-atom Ru species dispersed on zirconia-based catalysts. A DFT and FTIR study of CO adsorption”, ChemCatChem, 10, 2634-2645 (2018).

[5] L. De Rita, J. Resasco, S. Dai, A. Boubnov, H. V. Thang, A. S. Hoffman, I. Ro, G. W. Graham, S. R. Bare, G. Pacchioni, X. Pan, P. Christopher, “Structural evolution of atomically dispersed Pt catalysts dictates reactivity”, Nature Materials, 18, 746-751 (2019).

[6] H. V. Thang, G. Pacchioni, “Nature of atomically dispersed Ru on anatase TiO2: revisiting old data based on DFT calculations”, J. of Physical Chemistry C, 123, 7271-7282 (2019).

[7] H. V. Thang, G. Pacchioni, “On the real nature of Rh single-atom catalysts dispersed on the ZrO2 surface”, ChemCatChem, submitted.

Biography

Gianfranco Pacchioni is Vice-Rector for Research at the University of Milano Bicocca. He received the degree in Chemistry at the University of Milano (1978) and the Ph.D. in Physical Chemistry at the Free University of Berlin (1984). He has been working at the IBM Almaden Research Center in California (1987) and at the Technical University of Munich (1993). Associate Professor of Inorganic Chemistry at the University of Milano (1988), he is now Full Professor of Solid State Chemistry at the University of Milano Bicocca (since 2000).


He received various awards including the Nasini Medal (1994) and the Pisani medal (2017) of the Italian Chemical Society, the National Price “Federchimica” (1996), the Alexander von Humboldt Award (2005), the Blaise Pascal Medal of the European Academy of Sciences (2016). He is Fellow of the Accademia Nazionale dei Lincei (2014), the Academia Europaea (2012), and the European Academy of Sciences (2009).


He has been Chairman of the Department of Materials Science at the University of Milano Bicocca (2003-2009); of the COST Action “Inorganic oxide surfaces and interfaces” (2006-2010); of the Panel PE5 of the European Research Council for the Advanced Grants (2008-2012); of the Theoretical and Computational Chemistry Division of the Italian Chemical Society (2011-2013).
He is member of the Scientific Council or of the Board of several national and international institutions (Tronchetti Provera Foundation 2008-now; Consorzio CORIMAV for Advanced Materials 2004-now; EnergyLab Foundation 2009-2016; Lake Como School for Advanced Studies, 2015-now; KIC Raw Materials 2015-2018; Consiglio Nazionale delle Ricerche, 2016-now).
His main interests are theory and electronic structure of oxides (bulk, surface, thin films, nanostructures), supported metal clusters, materials for catalysis, photocatalysis and energy production. Gianfranco Pacchioni is co-author of about 500 papers with more than 22000 citations (h-index WoS: 79) and has given about 400 invited talks at international conferences and research institutions.


He has also been active in popularizing science and has published some books: “Scienza, quo vadis?” (Il Mulino, 2017), English edition by Oxford University Press under the title: “The Overproduction of Truth” (OUP, 2018); “Quanto è piccolo il mondo – Sorprese e speranze dalle nanotecnologie” (Zanichelli, 2007); “Idee per diventare scienziato dei materiali” (Zanichelli, 2005).

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