Oxidative Condensation of Methane in the Presence of Modified MnNaW/SiO2 Catalysts

摘要

The effects of cationic (Ce, Zr, and La) and anionic (S, P, and Cl) admixtures on the activity and physicochemical properties of MnNaW/SiO2 were studied in order to optimize the composition of a catalyst for the oxidative condensation of methane (OCM). It was found that OCM process characteristics can be regulated by varying the type (Ce, Zr, La, S, P, and Cl) and concentration (0.5-5 wt %) of a modifying admixture. For the modified MnNaW/SiO2 catalysts, the yield of the target reaction products increased in the following order of modifying admixtures: S < Zr < P < Ce < La < Cl. The addition of lanthanum, cerium, or phosphorus admixtures insignificantly affected the activity of the MnNaW/SiO2 catalyst, whereas the introduction of sulfur or zirconium led to a decrease in the yield of C-2 hydrocarbons. Modification with chlorine improved process characteristics and shifted a maximum yield of C-2 hydrocarbons to the low-temperature region. It was established that the introduction of lanthanum considerably improved the stability of catalyst operation. The catalyst composition 2Mn-1.6Na-3.1W-2La/SiO2 was developed to afford a 22% yield of target C-2 hydrocarbons at a 54% conversion of methane after a 24-h reaction performed under optimum conditions (reaction temperature, 800A degrees C; reaction mixture flow rate, 117 mL min(-1)g (Cat) (-1) and O-2/CH4 molar ratio, 0.5).