Relating Rates of Catalyst Sintering to the Disappearance of Individual Nanoparticles during Ostwald Ripening

Sintering of nanoparticles (NPs) of Ni supported on MgAl2O4 was monitored in situ using transmission electron microscopy (TEM) during exposure to an equimolar mixture of H-2 and H2O at a pressure of 3.6 mbar at 750 degrees C, conditions relevant to methane steam reforming. The TEM images revealed an increase in the mean particle size due to disappearance of smaller, immobile NPs and the resultant growth of the larger NPs. A new approach for predicting the long-term sintering of NPs is presented wherein microscopic observations of the ripening of individual NPs (over a span of a few seconds) are used to extract energetic parameters that allow a description of the collective behavior of the entire population of NPs (over several tens of minutes).