Diffuse Reflectance FT-IR Studies of the Adsorption of CO on Rh/Al 2 O 3 Catalysts

Abstract

The diffuse reflectance/FT-IR spectrum of CO/Rh/Al₂O₃ system has been investigated in terms of pretreatment of the catalyst, Rh loading, CO pressure (coverage), and coadsorption of CO with oxygen. The widths of all bands were narrowed by Fourier self-deconvolution (FSD), and six types of CO/Rh adsorbed species, including two which have not been assigned previously, have been identified by their C-O stretching frequencies. Species I, assigned to Rh(I)(CO)₂, is formed with isolated Rh atoms and/or edge Rh atoms of atomic “rafts” and/or atomic crystallites. Species II is assigned to Rh(O)-CO. Species III' is assigned to [Rh(O)|₂CO. Species VI is assigned to [Rh(I)]₂CO. Two new species—IIIa, assigned to [Rh(O)]₃CO, with underlying Rh atom, and VI', assigned to [Rh(I))₂(CO)₃—are postulated.