<p>A mordenite having improved carbonylation catalytic activity is prepared by treating a mordenite precursor of silica : alumina molar ratio of at least 10 : 1 with an aqueous ammonium hydroxide solution and recovering therefrom a mordenite having improved carbonylation catalytic activity. The mordenite is useful as a catalyst in the carbonylation of methanol and/or reactive derivatives thereof with carbon monoxide to produce acetic acid and/or methyl acetate.</p>
