Non‐oxidative Methane Activation over Molybdenum and Tungsten Nitride Catalysts

Abstract

AbstractIn this study, molybdenum (Mo), tungsten (W), and mixed metal oxide and ‐nitride catalysts are synthesized via incipient wetness impregnation on silica support (SBA‐15) with a total target metal loading of 4 wt %. The effect of the Mo : W ratio on the non‐oxidative methane conversion, product selectivity, and coke formation is evaluated. The reduced Mo/SBA‐15 and MoW/SBA‐15 catalysts show higher CH4 conversion activity to benzene (selectivity of ~75.5 %) than for ethylene (selectivity of ~9.5 %) with a rather fast coke formation rate of 19–24 mgCoke gCat−1 h−1 without a clear influence of the Mo : W ratio. In contrast, the metal nitrides have a much smaller coke formation rate. The smallest rate of 0.45 mgCoke gCat−1 h−1 is achieved for the WN/SBA‐15 sample, which increases with the molybdenum content to 4.7 and 8.6 mgCoke gCat−1 h−1 for the MoWN(5 : 1) and MoN/SBA‐15 catalysts, respectively. There seems to be a yet unknown but negative correlation between the coke formation rate and the number of silanamine functional groups formed during the catalyst nitridation (Si−OH→≡Si−NH2→≡Si−NH−Si≡). The C2H4 selectivity is significantly increased with the relative amount of tungsten, with the highest C2H4 selectivity of 63 % for mixed‐metal nitride catalyst containing Mo : W ratio of 1 : 5. While the Mo/SBA‐15 the MoN/SBA‐15 achieve a C2H4 selectivity of less than 10 %.