A detailed alkali catalytic preparation of diethyl carbonate (DEC) from diethyl oxalate (DEO) via gaseous phase decarbonylation was investigated in the paper. Evaluation results showed that 6wt% (based on potassium) K2CO3/AC (activated carbon) catalyst exhibited a relatively high catalytic activity. 54.3% conversion of DEC, 27.8% selectivity to DEC and 300.0g/(L h) space time yield of DEC were obtained at 513 K and the gas hourly space velocity 1000 h(-1). A series of characterization approaches were performed to explore the reasons for the decreasing catalytic activity. By means of XRD analysis, it can be concluded that the K2CO3 with high dispersion on the catalyst surface is favorable for the production of DEC, while the formation of K2CO3 crystallization results in the decrease of the catalytic activities. The KHCO3 crystallization detected on the catalyst surface after the reaction also leads to the degressive active properties. Moreover, the results of BET, XPS and ICP-OES indicated that the specific surface area and the potassium content of catalysts are closely related with the catalytic activity. (C) 2009 Elsevier B.V. All rights reserved.