In-situ characterization and beam effect studies of supported nanoparticle catalysts in the Environmental Transmission Electron microscope (ETEM)
Academic and industrial research both emphasized the need for studying catalysts under realistic conditions. Environmental transmission electron microscopy is a valuable tool to accomplish that and connect microscopic and macroscopic properties of materials by acquiring highly resolved local information under realistic environments, e.g. relating catalytic performance with crystal structure and morphology. At the same time it is essential to investigate and separate unintended electron beam induced changes observed in the samples from gas and temperature related ones. This talk will show several examples of the catalyst research performed at the Center for Electron Nanoscopy at the Technical University of Denmark (DTU Cen).
The catalysts used in this study are supported nanoparticles. The functionality of such nanoparticles is to a large extent controlled by their shape and exposed surface facets. However, information about the crystal structure of their surfaces is often obtained from measurements that are averaged over large numbers of particles. Furthermore, the catalytic activity depends on the support and hence on the interaction between support and catalyst nanoparticle.
This study presents characterization of the novel methanol catalysts NiGa and CuNi during catalyst formation, alcohol synthesis, and accelerated aging experiments. TEM is especially powerful in combination with other complimentary techniques. The in situ techniques used here were: (1) Activity measurements based on a reactor connected to a gas chromatograph (GC), (2) in situ x-ray diffractometer (XRD) measurements based on a reactor cell connected to a mass spectrometer, and (3) ETEM that allows for observation in a gaseous environment. Through the use of heating holders, dynamic information about catalysts close to their working state can be gained using a variety of TEM techniques [1,2].
Supported CuNi and Au nanoparticles on MgO nanocubes were also used for beam effect studies to investigate beam induced effects that are present in gaseous environment. These changes can occur both in shape and in chemistry of the involved crystals.
The combination of in-situ techniques successfully illustrates the capability of correlating the dynamic changes in structural phase and particle size distribution, measured both macroscopically (XRD) and microscopically (ETEM), with the catalytic activity.