I N D U S T R I A L R E S E A R C H

1 6 4 H I G H L I G H T S 2 0 2 1 I

PRINCIPAL PUBLICATION AND AUTHORS

Effect of thermal treatment on the stability of Na Mn W/SiO2 catalyst for the oxidative coupling of methane, D. Matras (a,b), A. Vamvakeros (c,d), S.D.M. Jacques (c), N. Grosjean (e), B. Rollins (e), S. Poulston (e), G.B.G. Stenning (f), H.R. Godini (g,h), J. Drnec (i), R.J. Cernik (a), A.M. Beale (b,c,d), Faraday Discuss. 229, 176-196 (2021); https:/doi.org/10.1039/C9FD00142E (a) School of Materials, University of Manchester (UK) (b) Research Complex at Harwell, Harwell Science and Innovation Campus, Rutherford Appleton Laboratory, Didcot (UK) (c) Finden Ltd, Abingdon (UK) (d) Department of Chemistry, University College London (UK) (e) Johnson Matthey Technology Centre, Sonning Common (UK) (f) ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot (UK) (g) Technische Universität Berlin, Berlin (Germany) (h) Department of Chemical Engineering and Chemistry, Eindhoven University of Technology (The Netherlands) (i) ESRF

Revealing the impact of high- temperature pre-treatment on catalyst performance with operando XRD-CT

The oxidative coupling of methane reaction has recently attracted a lot of attention as it provides a direct route for methane upgrading to higher value bulk chemicals, specifically ethylene, one of the key building blocks in the chemical industry.

One of the most promising catalysts for the oxidative coupling of methane (OCM) reaction is Mn-Na-W/SiO2. This catalyst is known to exhibit high performance, reaching up to 20% yield for ethane and ethylene under high operating temperatures (>750°C). However, there is limited information regarding the nature of the catalyst active species and their stability/evolution during long- term operation.

Operando X-ray diffraction computed tomography (XRD-CT) experiments were carried out at beamline ID31 to investigate the impact of thermal treatment on the catalyst structure and performance (Figure 143). Interlaced XRD-CT scans were acquired under varying operating conditions (i.e., temperature and gas composition) using a monochromatic beam of 70 keV and the PILATUS3 X 2M CdTe area detector. Each XRD-CT dataset was acquired every ca. 25 minutes and yielded reactor cross- section images with 224 × 224 pixels with a pixel size of 20 μm.

It was shown that the catalyst evolves at high temperatures, forming highly mobile and volatile Na W O Mn molten state species. By varying the parameters of the calcination protocol, it was shown that these molten components can be partially stabilised, resulting in a catalyst with lower activity (due to loss of surface area) but higher stability even for long-duration OCM reaction (>80 hr on stream).

Fig. 143: a) Operando XRD- CT experimental setup at beamline ID31. b) Schematic representation of catalytic reactor for the OCM reaction and representative XRD-CT image from the reactor cross-section.