Nickel supported on activated carbon can be used for the vapor phase carbonylation of methanol, producing methyl acetate and acetic acid as products. In contrast to previous reports, a strong influence of the support on the performance of the catalyst, in terms of both activity and stability, was observed in the current study. The effect appears to be related to the pore size distribution of the support. Catalysts prepared on large pore activated carbons are less active than catalysts prepared on smaller pore activated carbons but show no deactivation over time on stream. The mechanism of deactivation appears to be consistent with a strong adsorption of methanol and reaction products that plugs the catalyst pores and leads to increasingly strong diffusion limitations with time on stream. (C)2000 Elsevier Science B.V. All rights reserved.