UC Irvine

Catalysis remains an important field of research that drives economical approaches for various energy conversion applications from natural resources. Industrial catalyzed reactions occur at the surface of heterogeneous catalysts where many different active sites exist. Any atom not at the surface is not directly used to drive chemical reactions. To improve efficiency, catalytic nanomaterials have shrunk to the nano and atomic scale, increasing the surface area/volume ratio. Traditional characterization methods for nanomaterials provide a large scale picture of overall changes but do not exhibit a high degree of spatial information. To that end, transmission electron microscopy (TEM) may be used to probe materials down to the scale of individual atoms through both imaging and spectroscopy. Specialty holders allow for replication of benchtop reactions with which to investigate changes to nanomaterials in situ. Here, in situ TEM was used to gain insights into a variety of chemical processes including bond cleavage and surface reduction of different nanomaterials.First, we used in situ TEM to observe the contraction of the inter-metal center distances upon heating of a Zr based metal-organic framework before tracking the chemical bond changes with vibrational electron energy loss spectroscopy (EELS). The in situ results were corroborate with ex situ samples to validate the results. Then, in situ TEM and EELS was used to spatially map the Ce3+ aggregation on the surface of Pt loaded ceria nanoparticles. The localization of the Ce3+ had remained an unanswered question prior. The surface reduction was seen to proceed in an irreversible fashion which was attributed to orientated attachment, a precursor step to sintering. Finally, in situ TEM was performed in a liquid environment analyzing the growth of nanobubbles and the dissolution of octahedral core-shell nanoparticles. Both nanomaterials exhibited stages of structural changes that correspond to size stability and atom migration, respectively. As seen with the variety of nanomaterials observed, in situ TEM gives insight to the various chemical processes that occur when replicating benchtop reactions.