Catalysis and Chemistry

The ESRF is helping the chemical industry find more efficient and environmentally compatible processes for the manufacture of materials

Heterogeneous catalysis controls about 90% of the world’s chemical manufacturing processes, yet fundamental chemical and physical mechanisms are often not completely understood and its study remains largely empirical.
Synchrotron techniques at the ESRF offer unique opportunities to understand the behaviour of catalytic systems.
X-ray absorption spectroscopy provides information about the chemical bonds surrounding an absorbing atom, for instance, while qualitative and quantitative measurements during catalysis are possible at millisecond time resolution across all concentration ranges.

• Analyse the shape, size and density of particles including nanoparticles.

• Obtain 3D images of matrices and detect trace elements at high resolution.

• Determine quantitative oxidation states of species at ultra-dilute concentration.

• Study catalytic reactions such as the methanol-to-olefin process in situ and operando at extreme conditions and short timescales.

• Probe reaction intermediates.

• Characterise working batteries and fuel cells.

 

 

Company or institute

University of Torino in collaboration with Chimet SpA.

Challenge

To resolve the active species on the surface of a platinum catalyst during hydrogenation reactions.

Sample

The sample was an industrial 5 wt% Pt/Al2O3 catalyst of 1.4 nm Pt particle size. The model reaction studied was the hydrogenation of toluene to methylcyclohexane.

Solution

Multiple techniques were necessary to provide a complete picture of the hydrogenated Pt/Al2O3 catalyst. Firstly, inelastic neutron scattering (at ILL, Grenoble) was used to reveal the presence of n-fold coordinated platinum hydrides. FT-IR aided in identifying four linear platinum-hydride species, some of which form at the expense of the n-fold ones when the hydrogen concentration drops. It was confirmed by a combined DRIFTS/XAS/MS experiment at beamline BM23. The XAS part of this experiment (XANES and EXAFS)demonstrated that the Pt nanoparticles undergo a slow and progressive reconstruction upon hydrogenation/dehydrogenation. A second part of the study involved the hydrogenation of toluene, also followed by a combination of DRIFTS/XAS/MS. This demonstrated that the structure of the hydrogenated catalyst remained unchanged, with only surface species participating in the reaction.

Dehydrogenation of the Pt/Al2O3 catalyst during the operando DRIFTS/XAS/MS experiment

Dehydrogenation of the Pt/Al2O3 catalyst during the operando DRIFTS/XAS/MS experiment performed at BM23. a) Mass spectra evolution of hydrogen. b) 2D map showing the evolution of the DRIFT spectra. d-f) Evolution of the normalised Pt L3-edge XANES and EXAFS spectra of the Pt/Al2O3 catalyst collected simultaneously to the DRIFT spectra in part (b).

Benefits

The combination of techniques confirmed the reconstruction of the catalyst during activation and revealed the platinum-hydride species involved in catalytic hydrogenation and their interplay, which maintains a small proportion of the most active species available as the catalyst for the hydrogenation reaction.

Reference

Dynamics of reactive species and reactant-induced reconstruction of Pt clusters in Pt/Al2O3 catalysts, M. Carosso, E. Vottero, A. Lazzarini, S. Morandi, M. Manzoli, K.A. Lomachenko, M. Jimenez Ruiz, R. Pellegrini, C. Lamberti, A. Piovano, and E. Groppo, ACS Catalysis 9, 7124-7136 (2019); doi: 10.1021/acscatal.9b02079.