Dynamical Response of Catalytic Systems in a Cs Corrected Environmental TEM

Thomas W. Hansen
Funding: DTU Cen
In industrialized countries, 85-90% of chemical production involves catalytic processes. Transmission electron microscopy (TEM) has been used extensively in catalysis research. However, in contrast to chemical reactors, a conventional TEM is a high vacuum tool. Thus, observations do not always reflect the active state of materials. Environmental TEM (ETEM) provides the capability to expose samples to a gaseous atmosphere during imaging and analysis.Many catalytically active materials consist of metals or metal alloys, which are deposited onto a support material as nanoparticles to optimize the active surface area. In a catalytic reactor, the particles tend to sinter under reaction conditions (high temperature and pressure) resulting in the loss of active surface area and catalytic activity. Several models of the sintering process have been proposed based on investigations carried out post mortem, revealing only the final state of the catalyst, not the process as it happens. To investigate this phenomenon further a model system consisting of gold nanoparticles on a boron nitride support has been used and investigated in the ETEM. Mobility of the particles was clearly visible, while maintaining lattice resolution of both the BN support and the Au particles. The studies indicate that several processes are at work simultaneously. By quantifying these observations, fundamental insight into activation energies and energy barriers for sintering processes can be realised.

      

Frames extracted from a movie recorded in the Environmental TEM showing Au particles in a hydrogen atmosphere. The frames indicate how two particles with a diameter of ca. 5 nm merge into a single particle over time. 

Thomas Willum Hansen
Senior Researcher
DTU Cen
+45 45 25 64 76
http://www.cen.dtu.dk/english/research/projects/actual-dynamical-response-of-catalytic-systems-in-a-cs-corrected-environmental-tem
22 SEPTEMBER 2017