Real-time multi-length scale chemical tomography of fixed bed reactors during the oxidative coupling of methane reaction.

• X-ray tomographic chemical imaging of working catalysts. • Improving the chemical stability of Mn-Na-W/SiO 2 catalyst with La. • Insight into the multiple roles of the La-promoter. • Capturing the state of the active catalysts. In this work, we present the results from multi-length-scale studies of a Mn-Na-W/SiO 2 and a La-promoted Mn-Na-W/SiO 2 catalyst during the oxidative coupling of methane reaction. The catalysts were investigated from the reactor level (mm scale) down to the single catalyst particle level (μm scale) with different synchrotron X-ray chemical computed tomography techniques (multi-modal chemical CT experiments). These operando spatially-resolved studies performed with XRD-CT (catalytic reactor) and multi-modal μ-XRF/XRD/absorption CT (single catalyst particle) revealed the multiple roles of the La promoter and how it provides the enhancement in catalyst performance. It is also shown that non-crystalline Mn species are part of the active catalyst component rather than crystalline Mn 2 O 3 /Mn 7 SiO 12 or MnWO 4. [ABSTRACT FROM AUTHOR]