Environmental Transmission Electron Microscopy Study of the Origins of Anomalous Particle Size Distributions in Supported Metal Catalysts
Artikel i vetenskaplig tidskrift, 2012

In this Environmental Transmission Electron Microscopy (ETEM) study we examined the growth patterns' of uniform distributions of nanoparticles (NPs) using model catalysts. Pt/SiO2 was heated at 550 degrees C in 560 Pa of O-2 while Pd/carbon was heated in vacuum at 500 degrees C and in 300 Pa of 5%H-2 in Argon at temperatures up to 600 degrees C. Individual NPs of Pd were tracked to determine the operative sintering mechanisms. We found anomalous growth Of NPs occurred during the early stages of catalyst sintering wherein some particles started to grow significantly larger than the mean, resulting in a broadening of the particle size distribution (PSD). The abundance of the larger particles did not fit the log normal distribution. We can rule out sample nonuniformity as a cause for the growth of these large particles, since images were recorded prior to heat treatments. The anomalous growth of these particles may help explain PSDs in heterogeneous catalysts which often show particles that are significantly larger than the mean, resulting in a long tail to the right. It has been suggested previously that particle migration and coalescence could be the likely cause for such broad size distributions. We did not detect any random migration of the NPs leading to coalescence. A directed migration process was seen to occur at elevated temperatures for Pd/carbon under H-2. This study shows that anomalous growth of NPs can occur under conditions where Ostwald ripening is the primary sintering mechanism.

environmental

behavior

Pd/carbon

Pt/SiO2

surface

Ostwald ripening particle size distributions

coalescence

growth

nanoparticles

catalyst sintering

islands

heterogeneous catalysts

Författare

A. D. Benavidez

University of New Mexico

L. Kovarik

Pacific Northwest National Laboratory

A. Genc

FEI Company

N. Agrawal

Pacific Northwest National Laboratory

Elin Maria Kristina Larsson

Kompetenscentrum katalys (KCK)

Chalmers, Teknisk fysik, Kemisk fysik

T. W. Hansen

Danmarks Tekniske Universitet (DTU)

A. M. Karim

Pacific Northwest National Laboratory

A. K. Datye

University of New Mexico

ACS Catalysis

2155-5435 (eISSN)

Vol. 2 2349-2356

Ämneskategorier

Atom- och molekylfysik och optik

DOI

10.1021/cs3005117