ON THE MECHANISM OF CARBONYLATION IN ACETIC-ACID AND HIGHER ACID SYNTHESIS FROM METHANOL AND SYNGAS MIXTURES ON SUPPORTED RHODIUM CATALYSTS

In high pressure gas phase conditions, methanol and syngas mixtures ca n be converted to acetic and higher carboxylic (C-3-C-5) acids on supp orted rhodium catalysts in presence of methyl iodide. Chemical trappin g and FTIR spectroscopic studies show that two mechanisms are involved in the carboxylic acid formation. One is the conventional carbon mono xide insertion model on the rhodium part of the catalyst. The second p roceeds through the isomerization of methyl formate on the support. On the support alone the chain growth stops at the C-2-intermediate sinc e no rhodium is present to convert acetic acid or methyl acetate to et hanol or ethoxy species.