Complex structural dynamics of nanocatalysts revealed in Operando conditions by correlated imaging and spectroscopy probes

Y Li,S Zhao,R Tappero,D Zakharov,E.A Stach,Ph Baumann,U Jung,A.I Frenkel,R.G Nuzzo,A Elsen

doi:10.1038/ncomms8583

Abstract

Understanding how heterogeneous catalysts change size, shape and structure during chemical reactions is limited by the paucity of methods for studying catalytic ensembles in working state, that is, in operando conditions. Here by a correlated use of synchrotron X-ray absorption spectroscopy and scanning transmission electron microscopy in operando conditions, we quantitatively describe the complex structural dynamics of supported Pt catalysts exhibited during an exemplary catalytic reaction—ethylene hydrogenation. This work exploits a microfabricated catalytic reactor compatible with both probes. The results demonstrate dynamic transformations of the ensemble of Pt clusters that spans a broad size range throughout changing reaction conditions. This method is generalizable to quantitative operando studies of complex systems using a wide variety of X-ray and electron-based experimental probes.

Highlights

Understanding how heterogeneous catalysts change size, shape and structure during chemical reactions is limited by the paucity of methods for studying catalytic ensembles in working state, that is, in operando conditions
We quantitatively describe the complex structural dynamics exhibited by an exemplary catalytic reaction—ethylene hydrogenation carried out over supported Pt catalysts
The current work exploits a microfabricated catalytic reactor designed for correlated use with both synchrotron X-ray absorption spectroscopy and scanning transmission electron microscopy

Summary

Introduction

Understanding how heterogeneous catalysts change size, shape and structure during chemical reactions is limited by the paucity of methods for studying catalytic ensembles in working state, that is, in operando conditions. The results demonstrate dynamic transformations of the ensemble of Pt clusters that spans a broad size range throughout changing reaction conditions This method is generalizable to quantitative operando studies of complex systems using a wide variety of X-ray and electron-based experimental probes. The results demonstrate dynamic transformations of the ensemble of Pt clusters that spans from single atoms to large agglomerates throughout changing reaction conditions These heterogeneous materials are exceptionally complex from a structural perspective and, even for cases of carefully prepared model systems, may demonstrate a coexistence of different particle sizes, shapes, compositions and degrees of crystalline order within the metal clusters of the catalyst[6,7,8] This heterogeneity poses a formidable challenge to ensemble-averaging characterization techniques such as X-ray absorption fine structure (XAFS) spectroscopy, which collapses this structural heterogeneity into a single average measurement, albeit with exquisite spatial resolution[9]. Using the online gas analysis carried out at each facility (electron microscope and synchrotron beamline) during the chemical transformations in the micro-reactor, we can directly correlate the results at each stage of the reaction

Methods

Results

Conclusion