Visualizing single atom dynamics in heterogeneous catalysis using analytical in situ environmental scanning transmission electron microscopy

Abstract

Progress is reported in analytical in situ environmental scanning transmission electron microscopy (ESTEM) for visualizing and analysing in real-time dynamic gas–solid catalyst reactions at the single-atom level under controlled reaction conditions of gas environment and temperature. The recent development of the ESTEM advances the capability of the established ETEM with the detection of fundamental single atoms, and the associated atomic structure of selected solid-state heterogeneous catalysts, in catalytic reactions in their working state. The new data provide improved understanding of dynamic atomic processes and reaction mechanisms, in activity and deactivation, at the fundamental level; and in the chemistry underpinning important technological processes. The benefits of atomic resolution-E(S)TEM to science and technology include new knowledge leading to improved technological processes, reductions in energy requirements and better management of environmental waste. This article is part of a discussion meeting issue ‘Dynamic in situ microscopy relating structure and function’.

In situ visualisation and analysis of dynamic single atom processes in heterogeneous catalysts

“…12,16 To visualise and analyse single atom dynamics reliably in supported catalyst systems during chemical reactions in situ and in real time, an Environmental Scanning TEM (ESTEM) with single atom resolution and key additional analytical capabilities has been developed with an open aperture, gas-in-microscope design and constructed. 12,[15][16][17][18][19][20][21] Dynamic in situ experiments in the electron microscope benet from aberration correction (AC) to provide a series of unique single images, each at optimal and minimal defocus, with a continuous range of spatial frequencies, rather than requiring an impractical multi-image through-focal series.…”

“…12,[16][17][18] Currently, the majority of in situ aberration corrected (AC) ETEMS use the earlier in situ atomic resolution-ETEM design and development of Boyes and Gai, 2 described in the preceding sections. The development of the novel in situ AC ESTEM 12,[16][17][18][19][20][21] and its applications to nanoparticle catalysts [25][26][27][28][29] are highlighted in the following sections.…”

“…The new AC E(S)TEM system with single atom resolution operates in both ESTEM and ETEM modes, typically with <1 to >10 Pa gas pressures; in the latter case for a gas supply of [10 000 monolayers per second (>0.1 mbar) measured directly at the sample position with inlet gas pressures up to a few mbar. The gas supply is adequate to ood the sample surface with gas coverage, fully sufficient to drive the chemistry 12,[16][17][18][19][20][21][25][26][27][28][29][30] and catalysts are regularly activated in situ; as they may be in practical applications. In this context, Surface Science denes 'high pressure' as >0.1Pa (>0.001 mbar).…”

“…In the ESTEM experiments minimally invasive low dose electron beam techniques are used throughout. 12,[16][17][18][19][20][21][24][25][26][27][28][29] Data on in situ experiments under low electron dose conditions are checked in parallel with in situ data from 'blank' calibration experiments in which the dynamic experiments are conducted without the electron beam (by blanking the beam) and the beam is switched on only to record the nal reaction end point. In addition to providing direct and unparalleled insights into the dynamic evolution of structural changes and reaction mechanisms at the atomic level, the ESTEM and ETEM allow the detection, in real time, of surface as well as sub-surface structural phenomena.…”

Dynamic in situ microscopy relating structure and function

“…The goal is, therefore, to follow cycles to prepare, activate, react, deactivate, reactivate or recover precious materials—all under controlled conditions of a continuous gas atmosphere at operating temperature—combined with single-atom imaging and the highest quality analysis. Thus, a novel atomic resolution-environmental scanning transmission electron microscope (ESTEM), with a differentially pumped gas-in-microscope open aperture system, has been created [3] to access and analyse key processes in situ , with single-atom resolution under controlled dynamic reaction conditions. The aim is to provide a more accurate continuous characterization in situ during a dynamic reaction sequence and with it to supply a better-informed basis for the rational development of materials, process design and operation.…”