Activated carbon was used for the catalytic decomposition of dimethyl methylphosphonate (DMMP), a simulant of nerve gases, at various temperatures. Under the same conditions, activated carbon exhibited better longevity than a platinum catalyst, which has been widely chosen for this reaction. Nitrogen adsorption measurements at 77 K indicated that the majority of pores in the activated carbon were micropores, which could be transformed to macropores at 723 K in air. During the course of the reaction, large amounts of phosphorus species and coke occupied the pores, resulting in a sharp decrease in pore volume and surface area. Experimental results showed that the decomposition of DMMP involved two stages. In the first stage, activated carbon behaved as an initiator, converting DMMP into CO2, methanol, and P2O5. This reaction required oxygen supplied from air. In the second stage, P2O5 that had accumulated in the reactor was able to catalyze the decomposition of DMMP. The second stage was actually an autocatalytic process. A two-stage reaction model of DMMP decomposition on activated carbon and other catalysts is proposed. (C) 2001 Academic Press.