RESUMO
Prompt gamma activation analysis (PGAA) has been further developed to analyze reacting components inside a chemical reactor. The new method, in situ PGAA, was used to determine the hydrogen-to-palladium molar ratio under various conditions of palladium-catalyzed alkyne hydrogenation. The H/Pd molar ratio was successfully measured in the range of 0.1-1.0 in an approximately 2-g catalytic reactor containing a few milligrams of palladium catalyst. The amount of hydrogen was only a few tens of micrograms, and the detection limit was approximately 5 microg, i.e., at ppm level compared to the whole reactor. The description of the device, methodological developments, a feasibility study, and results of a series of catalytic measurements are presented.
RESUMO
We present a versatile grid reactor setup for transmission electron microscopy (TEM), which is able to track catalytic conversion on TEM amounts of sample. It is based on the concept of decoupling catalytic gas-phase reactions from the structural analysis of identical particles before and after reaction. The system has superior properties in terms of image resolution and long-term measurements compared to conventional in situ TEM analysis. Monitoring catalytic conversions on a TEM grid is enabled by proton-transfer reaction mass spectrometry. In addition, identical location imaging benefits from a secure transfer of the sample between TEM and the reactor system by vacuum transfer holders. Using Pt and Cu/ZnO/Al2O3 as an example we show that structural changes of identical particles or areas of a Pt foil before and after reactive experiments can be tracked. During catalytic testing the samples are exposed to homogeneous reaction conditions. The concept minimizes electron-sample and electron-atmosphere interactions and can prospectively be considered as complementary tool to in situ TEM analysis.