The Reactor-STM: A Real-Space Probe for Operando Nanocatalysis
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A Real-Space Probe for Operando Nanocatalysis Joost Frenken and Bas Hendriksen
Instrumentation Conventional Approach
Abstract “Looking” on the other side of the pressure gap in heterogeneous catalysis is an essential step in identifying and understanding differences and similarities between the behavior of catalysts under actual operation conditions (operando ) and under the nearvacuum conditions of traditional laboratory experiments. In this article, we demonstrate that real-space, atomic-scale imaging of active catalyst surfaces is possible under realistic or semirealistic reaction conditions with the reactor-STM, a scanning tunneling microscope that is fully integrated with a miniature flow reactor and housed inside an ultrahigh-vacuum system. This special-purpose instrument combines the merits of standard surface-science methods with operando STM observations of model catalysts in action. We illustrate the strength of this microscope with examples of CO oxidation on platinum surfaces.
Motivation for Scanning Tunneling Microscopy under Harsh Conditions Scanning tunneling microscopy and other forms of scanning probe microscopy form a family of experimental techniques that is, at least in principle, ideally suited for the investigation of model catalyst surfaces under the harsh conditions of industrial processes such as catalysis. This is important in view of the fact that the fundamental physics and chemistry of such processes have often been investigated only under highly artificial conditions, in particular, at very low pressures and relatively low temperatures, very distinct from those of the “real thing.”1 Although there are several documented cases in which low-P–low-T results can be extrapolated completely up to industrial conditions,2,3 the number of examples is growing where a “pressure gap” of, for example, 10 orders of magnitude between true process conditions and laboratory experiments is found to fundamentally change the process.4,5 Of similar importance is the large difference in geometry
cial design choices made in this firstgeneration instrument, after which we discuss a selection of experimental results obtained with it. The reactor-STM has enabled us to cast a first look at surfaces under combined high-pressure, hightemperature conditions with near-atomic resolution, and this has led to surprising new insights into the thermodynamics and kinetics of surfaces under these conditions. This article can be read as a review, but it should also be regarded as a progress report. The novelty and impact of the results obtained with the reactorSTM present a strong motivation for further improvement and expansion of the technique, which forms the subject of the outlook, provided near the end of the article.
and complexity between laboratory specimens and real catalysts, which is often referred to as the “materials gap.” Progress in these areas is strongly limited by the availability of experimental techniques that can investigate the active surfaces of catalysts or meaningful catalytic model systems wit
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