In the last decade the appearance of progressively more sophisticated codes, together with the increased computational capabilities, has made XANES a spectroscopic technique able to quantitatively confirm, or discard a structural model1 thus becoming a new fundamental diagnostic tool in catalysis, where the active species are often diluted metal centers supported on a matrix. After providing a brief historical introduction and the basic insights on the technique, in this seminar, I will provide a selection of four examples where operando XANES technique has been able to provide capital information on the structure of the active site. Among them: (i) Phillips catalyst for ethylene polymerization reactions;2 (ii) TS-1 catalyst for selective hydrogenation reactions;3 (iii) carbon supported Pd nanoparticles for hydrogenation reactions;4 (iv) Cu-CHA zeolite for NH3-assisted selective reduction of NOx and for partial oxidation of methane to methanol.5 The last example testifies how the multivariate curve resolution supported by the alternating least-squares algorithm applied to a high number of XANES spectra collected in operando conditions allows to quantitatively determine different species in mutual transformation. This approach is particularly powerful in the analysis of experiments where a large number of spectra has been collected, typical of time- or space-resolved experiments. Finally, machine learning approaches (both indirect and direct) have been applied to determine, from the XANES spectra, the structure of CO, CO2 and NO adsorbed on Ni2+ sites of activated CPO-27-Ni metal-organic framework.6
1. Guda, S. A.; et al. Optimized Finite Difference Method for the Full-Potential XANES Simulations: Application to Molecular Adsorption Geometries in MOFs and Metal-Ligand Intersystem Crossing Transients. J. Chem. Theory Comput. 2015, 11, 4512-4521.
2. Barzan, C.; et al. Ligands Make the Difference! Molecular Insights into CrVI/SiO2 Phillips Catalyst during Ethylene Polymerization. J. Am. Chem. Soc. 2017, 139, 17064-17073.
3. Braglia, L.; et al. Unpublished results.
4. (a) Bugaev, A. L.; et al. In situ formation of hydrides and carbides in palladium catalyst: When XANES is better than EXAFS and XRD. Catal. Today 2017, 283, 119-126. (b) Bugaev, A. L.; et al. Palladium Carbide and Hydride Formation in the Bulk and at the Surface of Palladium Nanoparticles. J. Phys. Chem. C 2018, 122, 12029-12037.
5. (a) Janssens, T. V.; et al. A consistent reaction scheme for the selective catalytic reduction of nitrogen oxides with ammonia. ACS Catal. 2015, 5, 2832-2845. (b) Lomachenko, K. A.; et al. The Cu-CHA deNOx Catalyst in Action: Temperature-Dependent NH3-Assisted Selective Catalytic Reduction Monitored by Operando XAS and XES. J. Am. Chem. Soc. 2016, 138, 12025-12028. (c) Martini, A.; et al. Composition-driven Cu-speciation and reducibility in Cu-CHA zeolite catalysts: a multivariate XAS/FTIR approach to complexity. Chem. Sci. 2017, 8, 6836-6851. (d) Pappas, D. K.; et al. Methane to Methanol: Structure–Activity Relationships for Cu-CHA. J. Am. Chem. Soc. 2017, 139, 14961–14975. (e) Pappas, D. K.; et al. J. Am. Chem. Soc. 2018, submitted.
6. Guda, S. A.; et al. Unpublished results.
Biography of Prof. Carlo Lamberti
Carlo Lamberti: born in 1964; degree in Physics in 1988; Ph.D. in solid state physics in 1993. He is professor in Physical Chemistry at the Torino University since 2006. He has performed more than 200 experiments with synchrotron and neutron sources at ADONE, LURE DCI and SuperACO, ESRF, Elettra, SRS, SLS, APS, SOLEIL, MAX-LAB, ISIS, SOLEIL, ILL, SINQ, FRM-II among them two Long Time projects at the ESRF and one at Elettra. He has been member of the review committees of ESRF and SLS. His research activities are focused in the multitechnical characterization of nanostructured materials under operation conditions. He edited the book Characterization of Semiconductor Heterostructures and Nanostructures, Elsevier, 2008 (second edition in 2013). He co-edited with J. A. van Bokhoven the book “X-Ray Absorption and X-ray Emission Spectroscopy: Theory and Applications”, Wiley 2016. He has authored and coauthored more than 350 research papers, 17 review articles, 20 book chapters, that have received more than 19000 (24000) citations with an h-index of 75 (87) according to ISI WoS (Google Scholar). He is the Italian coordinator of the European master in Materials Science MaMaSELF (https://www.mamaself.eu/) Between Torino, Rennes-1, Montoellier-2, LMU and TUM universities. He is member of the PhD School in Chemical and Materials Sciences, he has been the president of the Master in Materials Science and was the Director of the interdepartmental center CrisDi for crystallography. From 2014 he is the PI of the Mega-grant 14.Y26.31.0001 of the Russian Federation Government at the Southern Federal University in Rostov-on-Don where he is the Scientific Director of the Smart Materials international research Institute.