Carbonylation of Methanol over Supported Rhodium Catalysts

Abstract

Rhodium on different supports was found to be the most active and selective among supported transition metal catalysts for the vapor phase carbonylation of methanol and hydrocarboxylation of ethylene. High catalyst activities and good selectivities were obtained for the carbonylation of methanol over carbon supported rhodium catalysts in tubular reactor. A detailed parameter study of the carbonylation reaction, led to the experimental establishment of the kinetic equation. Fourier transform infrared (FT-IR) transmission spectroscopy was used to verify the validity of homogeneous methanol carbonylation mechanisms for two-phase (vapor-solid) applications. FT-IR spectra of adsorbed species obtained on RhCl₃/Cab-O-Sil 5 catalyst treated successively with CO₁ CH₃I and CH₃OH gave valuable information on the reaction mechanism. The absorption band appearing at 1717–1723 cm-₁ after adsorption of CH₃I on the catalyst surface is close to the acetyl C=O stretching freq (1708–1711 and 1723 cm’_-1) obtained under homogeneous conditions, proving that the surface complex of type [Rh(CO)₂Acl_xL_v]’ (Ac = CH₃CO^-, L = OH^- H₂0, SiO^-, and x + y = 3) can be assumed as reaction intermediate, and the similarity of the mechanisms in both liquid and vapor-solid reaction conditions as well.