Fischer-Tropsch catalysts are used to synthesize hydrocarbons from syngas (H2 + CO), and the addition of promoters can improve catalytic activity and affect selectivity. The exact chemical nature of active sites is still under debate, and nanoscale mechanisms for catalyst failure are not well understood. Operando imaging of hierarchical functional materials [1] using spectrocopic full-field imaging at 30 nm resolution can be used to correlate mesoscale heterogeneities in chemistry and morphology, providing insight into mechanisms for function and failure. We have collected single-pixel Fe K-edge [2] and Co K-edge XANES [3] of Fischer-Tropsch catalysts, using a specially designed reactor to perform operando F-T synthesis under full reaction conditions including temperature (to 450 C) and pressure (10 bar), to examine heterogeneity of active forms within the catalysts. We will present results on structure-performance relationships that provide insight into activity and failure mechanisms in these reactions.  Figure 1: a) Snapshots of 3D elemental mapping of fresh FT catalyst (Fe = red, Zn = green, Ti + K = yellow). (b) 2D chemical maps from single-pixel (30 nm resolution) XANES imaging of fresh catalyst, and after 4 and 7 h under reaction conditions. (b3-b5) Single pixel Fe K-edge spectra from 3 regions. Experimental data (�); fitted data (�) [2].References  [1]  J.C. Andrews and B. M. Weckhuysen, ChemPhys Chem (2013) DOI: 10.1002/cphc.201300529[2]  I. Gonzalez-Jimenez et al, Angew. Chem. Int. Ed.51 , 11986 (2012).[3]  K.H. Cats et al, Chem. Commun. 49 , 4622 (2013).* jandrews@slac.stanford.edu

Imaging nanoscale heterogeneities in operando Fischer-Tropsch catalysis

247th National Meeting (2014)

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