In this thesis, 13 types of M – Na – Mn / SiO 2 catalysts, (M = W, V, Mo, Nb, Cr) have been prepared by incipient wetness impregnation method and their catalytic performance for oxidative coupling of methane (OCM) to C 2 hydrocarbons (C 2 H 4 and C 2 H 6 ) was examined. The catalysts are prepared by sequential impregnation of aqueous solution of metal salts and then manganese nitrate on the silica followed by drying and calcinations at 850 °C for 6h. the catalytic performance was evaluated in a continuous - flow micro reactor at atmospheric pressure, an operating temperature of 775 °C, a gas hourly space velocity (GHSV) of 2500 ml hr -1 g -1 , and a CH 4 / O 2 / N 2 = 2 / 2/ 1. The structural properties of the catalysts have been studied using X-ray diffraction (XRD), laser Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), surface area by BET method, and temperature programmed reduction (TPR) with H 2 . The used catalysts also were characterized with XRD and BET. The results of the catalytic performance revealed that promoter (sodium salts containing different oxo anions) largely influence the C 2 selectivity of the catalysts. C 2+ selectivity (or C 2+ yield) increase with the transition metal compound of the catalysts in the order of W Mo Cr Nb V in the range of 4 – 46 % while the catalytic conversion changed in the range of 28 – 46 %. Catalyst characterization results indicated that manganese oxide (Mn 2 O 3 ) and ?-cristobalite were the predominant species in the surface catalysts. Na + ion, as a structural promoter led to transformation of amorphous SiO 2 exclusively to ?-cristobalite, and increased surface basicity. The concentration of Mn in the catalyst played an important role, as increase in manganese concentration in W – Na – Mn / SiO 2 catalyst led to higher yield from 14 % to 18 %. Increase in sodium salt concentration led to higher yield of W – Na – Mn / SiO 2 catalyst from 14 % to 18 % and lower yield of Mo – Na – Mn / SiO 2 catalyst from 14 % to 12 %. Presence of hot spot in the catalyst bed led to destroy the structure and changed ?-cristobalite into SiO 2 quartz and decreased the crystalline size. Also catalysts used for methane coupling deactivate slowly due to sintering in which after 9 hr of reaction at 775 °C, the surface area decreased from 2.34 m 2 g -l to 0.0584 m 2 g -1 . The structural and catalytic performance results revealed that Mn 2 O 3 species acted as an active site in the catalyst