FisMat2017 - Submission - View

Abstract's title: The potential of multivariate analysis of in situ XAS data: applications to Cu-zeolite nano-catalysts
Submitting author: Elisa Borfecchia
Affiliation: Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin
Affiliation Address: Via P. Giura 7, 10126, Torino
Country: Italy
Oral presentation/Poster (Author's request): Oral presentation
Other authors and affiliations: Andrea Martini (Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin, Turin, Italy), Kirill A. Lomachenko (European Synchrotron Radiation Facility,Grenoble Cedex, France. IRC “Smart Materials”, Southern Federal University, Rostov-on-Don, Russia), Chiara Negri (Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin, Italy), Gloria Berlier (Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin, Turin, Italy), Pablo Beato (Haldor Topsøe A/S, Kgs. Lyngby, Denmark), Hanne Falsig (Haldor Topsøe A/S, Kgs. Lyngby, Denmark), Carlo Lamberti (Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin, Turin, Italy. IRC “Smart Materials”, Southern Federal University, Rostov-on-Don, Russia), Silvia Bordiga (Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin, Turin, Italy)
Abstract

Cu-exchanged chabazite (Cu-CHA) is currently the object of intensive research efforts in the field of NH3-assisted selective catalytic reduction (SCR) of NOx [1] and direct conversion of methane to methanol [2]. Accessing structural and electronic information on the Cu-species formed during activation and in reaction condition is fundamental to unleash the potential of these promising nano-catalysts.

In this context, our joined academic/industrial team has widely employed in situ/operando X-ray absorption (XAS) a to shed light on the Cu-species hosted in Cu-CHA during activation and in SCR-relevant conditions [3]. In the recent literature [3, 4], it has become evident that the structural/electronic properties and location of Cu-species in Cu-zeolites is strongly influenced by composition (Si/Al and Cu/Al ratios) and environmental conditions, such as temperature and gas feed composition. Advanced in situ/operando characterization approaches and appropriate analytic tools allowing to manage complex spectroscopic datasets are thus mandatory to properly address the fickle nature of the active metals sites as well as to catch the dynamic host-guest interactions in these fascinating nano-materials.

In this contribution we demonstrate the potential of multivariate analysis in the rationalization of a large (ca. 100 spectra) in situ XAS dataset collected on a multi-composition platform of Cu-CHA catalysts during the activation process in inert gas flow. The study was aimed to clarify the influence of the catalyst composition on the temperature-dependent Cu-speciation and reducibility. After principal component analysis of the temperature-dependent XANES dataset, we applied a multivariate curve resolution (MCR) approach [5] to extract chemically-meaningful spectra and concentration profiles of pure components formed during He-activation as a function of the catalyst composition.Based on the spectroscopic fingerprints of each theoretical XANES and the correspondent temperature-dependent concentration profiles, we were able to assign the theoretical spectra to pure Cu-species/sites. For the first time, this approach allowed us to rationalize in a quantitative frame the complex dynamics of Cu-cations in the CHA cages during the activation process [6].

[1] U. Deka et al., ACS Catal. 2013, 3, 413-427. A.M. Beale et al., Chem. Soc. Rev. 2015, 44, 7371-7405.

[2] M.J. Wulfers et al., Chem. Commun. 2015, 51, 4447-4450. K. Narsimhan et al., ACS Cent. Sci. 2016, 2, 424-429.

[3] E. Borfecchia et al., Chem. Sci. 2015, 6, 548-563. T.V.W. Janssens et al., ACS Catal. 2015, 5, 2832-2845; K.A. Lomachenko et al., J. Am. Chem. Soc. 2016, 138, 12025-12028.

[4] C. Paolucci et al., J. Am. Chem. Soc. 2016, 138, 6028-6048.

[5] E. R. Malinowski, Factor Analysis in Chemistry, Wiley (2002); J. Jaumot et al., Chemometr. Intell. Lab. 2015, 140, 1-12.

[6] A. Martini, et al., Chem. Sci., under review.