Synthesis and characterization of rhodium oxide nanoparticles in mesoporous MCM-41

Rhodium-containing MCM-41 mesoporous molecular sieves (Rh-MCM-41) were synthesized by adding RhCl3·3H2O to a mixed silicate–surfactant gel prior to hydrothermal synthesis. The obtained Rh-MCM-41 samples were characterized by XRD, N2 adsorption, TEM, 29Si solid-state NMR and XPS. It was found that rhodium oxide nanoparticles <3 nm were located in the MCM-41 mesopore channels or 6 nm rhodium oxide particles were dispersed in the MCM-41 matrices, depending on the hydrothermal synthesis temperature and the aging conditions. The unit cell and pore wall thickness of Rh-MCM-41 synthesized at 423 K were 5.71 and 2.31 nm, respectively, which were larger than those of the corresponding pure Si-MCM-41. The increase in the pore wall thickness may be due to enhancement of cross-linking of â–·Si–OH in the silicate gel by the presence of Rh ions.