Supported Rh/Al2O3 and Rh/TiO2 catalysts with varying metal loadings were investigated by chemisorption and temperature-programmed reduction and oxidation. Hydrogen chemisorption showed that all the Rh on Al2O3 was well dispersed (H/Rh > 1 for loadings below 5 wt% and H/>Rh > 0.5 up to 20 wt%), while the dispersion on TiO2 was much lower. TPR/TPO showed that this was due to the growth of two different kinds of Rh/Rh2O3 particles on TiO2; one kind was easily reduced/oxidized, with a high dispersion, and the other kind was harder to reduce/oxidize, with a lower dispersion. TEM showed that the first kind of Rh2O3 consisted of flat, raftlike particles and the second kind of spherical particles.
Vis, J. C., Blik, van 't, H. F. J., Huizinga, T., Grondelle, van, J., & Prins, R. (1985). The morphology of rhodium supported on TiO2 and Al2O3 as studied by temperature-programmed reduction-oxidation and transmission electron microscopy. Journal of Catalysis, 95(2), 333-345. https://doi.org/10.1016/0021-9517%2885%2990111-3, https://doi.org/10.1016/0021-9517(85)90111-3