Metal Nanocatalyst Sintering Interrogated at Complementary Length Scales

Abstract

Metal nanoparticle (NP) sintering is a prime cause of catalyst degradation, limiting its economic lifetime and viability. To date, sintering phenomena are interrogated either at the bulk scale to probe averaged NP properties or at the level of individual NPs to visualize atomic motion. Yet, “mesoscale” strategies which bridge these worlds can chart NP populations at intermediate length scales but remain elusive due to characterization challenges. Here, a multi‐pronged approach is developed to provide complementary information on Pt NP sintering covering multiple length scales. High‐resolution scanning electron microscopy (HRSEM) and Monte Carlo simulation show that the size evolution of individual NPs depends on the number of coalescence events they undergo during their lifetime. In its turn, the probability of coalescence is strongly dependent on the NP's mesoscale environment, where local population heterogeneities generate NP‐rich “hotspots” and NP‐free zones during sintering. Surprisingly, advanced in situ synchrotron X‐ray diffraction shows that not all NPs within the small NP sub‐population are equally prone to sintering, depending on their crystallographic orientation on the support surface. The demonstrated approach shows that mesoscale heterogeneities in the NP population drive sintering and mitigation strategies demand their maximal elimination via advanced catalyst synthesis strategies.

Controlling Pt nanoparticle sintering by sub-monolayer MgO ALD thin films

“…36,40,41 Therefore, a shift of the main scattering feature to lower q y values points at an increase in NP spacing and is indicative of NP sintering. 36,38…”

“…36,40,41 Therefore, a shift of the main scattering feature to lower q y values points at an increase in NP spacing and is indicative of NP sintering. 36,38 The method used to extract the q y,max value of the 2D GISAXS patterns is detailed in Fig. S12, † and the results are depicted in Fig.…”

“…Samples are annealed to 800 °C in a custom-built vacuum chamber with a dedicated high-temperature heating stage. 37,38 The heater is controlled with a Eurotherm PID regulator. The chamber is evacuated to 10 −2 mbar and then filled to 1 bar with a mixture of 20% O 2 (99.999%) in He (99.999%) using a continuous flow of 500 sccm set using a mass flow controller system (MKS instruments).…”

Nanoscale Chemical Diversity of Coke Deposits on Nanoprinted Metal Catalysts Visualized by Tip‐Enhanced Raman Spectroscopy

“…Particularly, disordered coke burns at significantly lower temperatures compared to graphitic coke during O 2 reactivation. [9] Lowering the reactivation temperature will thus free-up the Pt surface necessary for reaction, but simultaneously prevent significant nanoparticle sintering inherently connected to high-temperature O 2 reactivation, [17,67,68] thus extending the catalyst lifetime. In general, the demonstrated approach paves the way to a more general application of TERS on nonconductive catalyst surfaces, such as zeolites and metal (oxide) catalysts, a field which is yet to be explored.…”

Investigating Palladium Nanoparticle Morphogenesis on Zeolite for Passive NOx Adsorption via In Situ Transmission Electron Microscopy Analysis under Hydrothermal Conditions

“…High temperatures typically induce movement of metal nanoparticles and of atomic species. Generally speaking, such movements often result in Ostwald-ripening sintering mechanisms. , Smaller particles are fragmented (potentially down to single atoms) and used in favor of increasing the size of larger particles, which decreases the available surface area and results often in a loss of performance. A common strategy to prevent sintering is by entrapping the metal atoms in microporous materials.…”