  Sintering refers to particle coalescence by heat, which has been known as a
thermal phenomenon involving all aspects of natural science for centuries. It
is particularly important in heterogeneous catalysis because normally sintering
results in deactivation of the catalysts. In previous studies, the enthalpy
contribution was considered to be dominant in sintering and the entropy effect
is generally considered neglectable. However, we unambiguously demonstrate in
this work that entropy could prevail over the enthalpy contribution to dominate
the sintering behavior of supported nanoparticles (NPs) by designed experiments
and improved theoretical framework. Using in situ Cs-corrected environmental
scanning transmission electron microscopy and synchrotron-based ambient
pressure X-ray photoelectron spectroscopy, we observe the unprecedent
entropy-driven phenomenon that supported NPs reversibly redisperse upon heating
and sinter upon cooling in three systems (Pd-CeO2, Cu-TiO2, Ag-TiO2). We
quantitatively show that the configurational entropy of highly dispersed
ad-atoms is large enough to reverse their sintering tendency at the elevated
temperature. This work reshapes the basic understanding of sintering at the
nanoscale and opens the door for various de-novo designs of thermodynamically
stable nanocatalysts.
