18 research outputs found
In situ observation of oscillatory redox dynamics of copper
How a catalyst behaves microscopically under reaction conditions, and what kinds of active sites transiently exist on its surface, is still very much a mystery to the scientific community. Here we present an in situ study on the red-ox behaviour of copper in the model reaction of hydrogen oxidation. Direct imaging combined with on-line mass spectroscopy shows that activity emerges near a phase boundary, where complex spatio-temporal dynamics are induced by the competing action of simultaneously present oxidizing and reducing agents. Using a combination of in situ imaging with in situ X-ray absorption spectroscopy and scanning photoemission microscopy, we reveal the relation between chemical and morphological dynamics and demonstrate that a static picture of active sites is insufficient to describe catalytic function of redox-active metal catalysts. The observed oscillatory redox dynamics provide a unique insight on phase-cooperation and a convenient and general mechanism for constant re-generation of transient active sites
Complex structural dynamics of nanocatalysts revealed in Operando conditions by correlated imaging and spectroscopy probes
Detecting and utilizing minority phases in heterogeneous catalysis
Highly active phases in carbon monoxide oxidation are known, however they are transient in nature. Here, we determined for the first time the structure of such a highly active phase on platinum nanoparticles in an actual reactor. Unlike generally assumed, the surface of this phase is virtually free of adsorbates and co-exists with carbon-monoxide covered and surface oxidized platinum. Understanding the relation between gas composition and catalyst structure at all times and locations within a reactor enabled the rational design of a reactor concept, which maximizes the amount of the highly active phase and minimizes the amount of platinum needed
Phase contrast scanning transmission electron microscopy imaging of light and heavy atoms at the limit of contrast and resolution
Evolution and stabilization of subnanometric metal species in confined space by in situ TEM
Understanding the behavior and structural transformation of metal species under reaction conditions is instrumental for developing more efficient and stable catalysts. Here, the authors reveal the evolution and stabilization of subnanometric Pt species confined in MCM-22 zeolite using in situ transmission electron microscopy