Structure of catalytically active Rh-In bimetallic phase for amination of alcohols

The structure of Rh-In bimetallic catalysts supported on carbon for amination of alcohols was determined by XRD, TEM-EDX, XPS, CO adsorption and EXAFS. At low In/Rh ratio (In/Rh ≤ 0.2), Rh metal particles with sizes of <3 nm were observed, and the particles were partially covered with indium oxide species. With addition of more In, a tetragonal RhIn alloy with a particle size of ∼20 nm was formed. This tetragonal alloy has a structure with a = 0.315 nm and c = 0.328 nm where metal atoms are located at (0, 0, 0) and (0.5, 0.5, 0.5). The catalytic activity of the tetragonal RhIn alloy is much higher than that of Rh metal particles with or without indium oxide species. With an excess amount of In (In/Rh > 1) on the high Rh loading (20 wt%) catalyst, the cubic RhIn phase with a CsCl structure was observed instead of the tetragonal RhIn phase, and the catalytic activity was much decreased.