In Situ TEM Study of the Genesis of Supported Nickel Catalysts

Abstract

In situ transmission electron microscopy is a powerful technique with the unique ability to temporally and spatially resolve nanoscale processes. This can be leveraged in order to obtain insight into the timescales of phenomena occurring during particle growth during the preparation of supported metal catalysts. Thanks to careful experimental design and comparison with ex situ results, the growth of individual nickel nanoparticles from a nickel phyllosilicate catalyst precursor during reduction was studied in situ under atmospheric pressure of 5% H2/Ar at 500 °C and modeled with first-order reaction kinetics. Particles grew rapidly, reaching a final size of between 3.5 and 7 nm within 3–4 min. The vast majority of particles grow as immobile single particles. A two-step particle growth mechanism was sometimes observed wherein two particles nucleating sufficiently close to one another sintered. The resulting particles were not significantly larger (5–7 nm) than those that did not undergo this sintering process. This finding supports the hypothesis that the size of the region from which the nickel species originated determined the particle size.

Direct Observation of Ni Nanoparticle Growth in Carbon-Supported Nickel under Carbon Dioxide Hydrogenation Atmosphere

“…This step was important not only to reduce the passivated Ni­(O) particles but also to remove water from the holder and the support surface. The removal of remaining traces of water before exposure to the electron beam was crucial to prevent support damage due to the formation of radicals. ,, Subsequently the chip was cooled down to 150 °C and briefly exposed to the electron beam to find suitable areas for imaging and perform alignment. The beam was then blanked and the gas was switched to 4:1 H 2 /CO 2 , which was mixed in the manifold using pure CO 2 (purity N = 5.3) and pure H 2 (purity N = 7.0), with a flow rate of 0.4 sccm.…”

“…Reproducing the same behavior of a catalyst from a reactor setup in an in situ TEM holder is not evident. , The performance of a catalyst is affected by factors such as temperature, gas hourly space velocity (GHSV), grain size, and type of reactor used. Thus, differences in the flow dynamics of a gas cell compared to a catalytic reactor can affect the observed results . Moreover, the nature of supported nanoparticles with nonstructured, high-surface-area supports used for heterogeneous catalysis makes it inherently challenging to analyze these catalysts with electron microscopy and in particular during in situ studies.…”

Advances and Opportunities in Closed Gas-Cell Transmission Electron Microscopy

“…This abnormal growth mechanism not only highlights stability of Pt 3 Co in oxidizing environments but also challenges conventional knowledge by demonstrating that oxygen annealing can precisely design Pt–M core–shell structures for ORR catalysis. Similarly, the size, morphological, and atomic structure evolution of different catalysts have been analyzed to provide guidance for synthesis, which includes supported Ni, Pt-based NPs and nanowires, Ce 0.2 Zr 0.8 O 2 , Pd and Pd–Cu nanocrystals, , and a zeolite imidazole framework, among others. These studies significantly advance our understanding of catalyst synthesis and contribute to the development of theoretical models …”