In Situ TEM Study of Rh Particle Sintering for Three-Way Catalysts in High Temperatures

One of the main factors in the deterioration of automobile three-way catalysts is the sintering of platinum group metals (PGMs). In this study, we used in situ tunneling electron microscopy (TEM) to examine the sintering of Rh particles as the temperature increases. Two types of environmental conditions were tested, namely, vacuum atmosphere with heating up to 1050 degrees C, and N-2 with/without 1% O-2 at 1 atm and up to 1000 degrees C. Under vacuum, Rh particles appeared to be immersed in ZrO2. In contrast, at 1 atm N-2 with or without 1% O-2, the sintered Rh particles appeared spherical and not immersed in ZrO2. The latter trend of Rh sintering resembles the actual engine-aged catalyst observed ex situ in this study. In the N-2 atmosphere, the sintering of support material (ZrO2 or Y-ZrO2) was first observed by in situ TEM, followed by Rh particle sintering. The Rh particle size was slightly smaller on Y-ZrO2 compared to that on ZrO2. To better understand these experimental results, density functional theory was used to calculate the systems' junction energies, assuming three layers of Rh(111) 4 x 4 structures joined to the support material (ZrO2 and Y-ZrO2). The calculated energies were consistent with the in situ TEM observations in the N-2 atmosphere.

Automated summary

The study investigated the sintering of Rh particles using in situ tunneling electron microscopy as the temperature increases, revealing different sintering behaviors in vacuum and N-2 atmospheres. In N-2 atmosphere, the sintering of support material was observed first before Rh particle sintering. The calculated junction energies were consistent with in situ TEM observations in the N-2 atmosphere.