Sample Environment for Operando Hard X-ray Tomography—An Enabling Technology for Multimodal Characterization in Heterogeneous Catalysis

Johannes Becher,Sakura Pascarelli,Dario Ferreira Sanchez,Thomas L Sheppard,Debora Motta Meira,Gerald Falkenberg,Jan-Dierk Grunwaldt,Sebastian Weber,Jan Garrevoet,Dmitry E Doronkin

doi:10.3390/catal11040459

Abstract

Structure–activity relations in heterogeneous catalysis can be revealed through in situ and operando measurements of catalysts in their active state. While hard X-ray tomography is an ideal method for non-invasive, multimodal 3D structural characterization on the micron to nm scale, performing tomography under controlled gas and temperature conditions is challenging. Here, we present a flexible sample environment for operando hard X-ray tomography at synchrotron radiation sources. The setup features are discussed, with demonstrations of operando powder X-ray diffraction tomography (XRD-CT) and energy-dispersive tomographic X-ray absorption spectroscopy (ED-XAS-CT). Catalysts for CO2 methanation and partial oxidation of methane are shown as case studies. The setup can be adapted for different hard X-ray microscopy, spectroscopy, or scattering synchrotron radiation beamlines, is compatible with absorption, diffraction, fluorescence, and phase-contrast imaging, and can operate with scanning focused beam or full-field acquisition mode. We present an accessible methodology for operando hard X-ray tomography studies, which offer a unique source of 3D spatially resolved characterization data unavailable to contemporary methods.

Highlights

The aRCTIC setup was designed for use at hard X-ray microscopy beamlines operating with either focused scanning beam or full-field imaging modes but may be adapted for spectroscopy and scattering beamlines
An illustration of aRCTIC installed at beamline
Precise control of gas and temperature conditions allows for meaningful quantitative gas-phase activity tests combined with tomography

Summary

Introduction

While in situ and operando studies are commonplace, often these are coupled to averaging measurements, which only address global sample composition (e.g., powder X-ray diffraction (XRD), diffuse reflectance infrared spectroscopy (DRIFTS), or X-ray absorption spectroscopy (XAS)) This can be problematic since samples in heterogeneous catalysis are typically rather complex or hierarchically structured. These may consist of composite materials or contain diverse macroscopic features, internal pore networks on the μm to nm scale, together with active catalytic sites (e.g., metal nanoparticles, clusters), and various support or spectator phases [8,9,10] Due to this intrinsic heterogeneity, comprehensive in situ and operando analysis of a target catalyst or process should ideally cover all relevant length scales [11,12,13] and ideally include both global and spatially resolved measurements to produce meaningful results regarding local sample structure [14,15]. The more accurate and realistic the characterization in spatial and time domains and in terms of reaction conditions, the more information can be harvested regarding structure–activity relationships

Methods

Results

Conclusion