A long-term stable Cu/Ni/SiO2 catalyst for carbon dioxide reforming of methane to produce synthesis gas at 800 degreesC was developed. The stability of the Cu/Ni catalysts depends on the reaction temperature and Cu/Ni ratio. Temperature programmed oxidation and temperature programmed reaction with CO2 were applied to Ni and Cu/Ni catalysts to study the effect of Cu on Ni catalyst. The stability can not be fully explained by the ensemble effect of the Cu on Ni metal that may inhibit the carbon formation rate on Ni catalyst. Copper may stabilize the structure of the active site on Ni surface for methane cracking reaction, preventing the deactivation of the Ni catalyst caused by sintering or by loss of nickel crystallites. The addition of Cu into Ni catalyst system can fine-tune the catalytic activity so that the CH4 cracking and removal of coke by CO2 is balanced and prevent inactive coke accumulation on Ni particle. Thus encapsulated carbon layer does not formed on supported Cu/Ni giving the catalyst a stable activity. (C) 2004 Elsevier B.V. All rights reserved.