A vapor phase process for the carbonylation of lower alkyl alcohols to esters and optionally, carboxylic acids using a catalyst containing iridium and at least one second metal selected from the Lanthanide Series. Desirably, the iridium and secondary metal are deposited on activated carbon as a support material. In a preferred aspect of the invention, the vapor phase process is useful for preparing acetic acid, methyl acetate or a mixture thereof by contacting the catalyst with a vapor comprising methanol, a halide and carbon monoxide under carbonylation process conditions.