“…3, the Rh particle was directly fastened to SiO 2 by interaction of Rh and SiO 2 (Rh O bonds) after calcination and most Rh species at the outer layer of Rh nano-particle were reduced to Rh 0 species. After they had been chemically adsorbed by PPh 3 , these Rh 0 species at the surface were oxidized to Rh δ+ (0 < δ < 1) species by syngas and bound to the Rh 0 layer in the bulk of metallic nanoparticles, and all these exterior Rh species were tightly bound by the very strong metal-metal bonds [31]. When the coordination bonds between Rh δ+ and ligands are broken during catalytic reactions, Rh species is fixed on SiO 2 by the Rh O bonds and the very strong metal-metal bonds and PPh 3 is inevitably leached in the case of PPh 3 -Rh/SiO 2 , however, the Rh ion may break away from the support in a homogeneous catalyst heterogenized on a solid support [21].…”