Synthesis of Light Hydrocarbons via Oxidative Coupling of Methane over Silica-supported Na2WO4-TiO2 Catalyst

Abstract

Methane is of great interest for conversion into high-value hydrocarbons (C2+) and olefins, via oxidative coupling of methane (OCM) using catalysts. In this work, Na2WO4-TiO2/SiO2 catalyst, along with the single catalysts of its components (Na2WO4/SiO2 and TiO2/SiO2), was investigated for OCM reaction to C2+. We found that 5 wt% Na2WO4+ 5 wt% TiO2 on the SiO2 support was a superior catalyst for OCM reaction compared to the single catalysts. The maximum C2+ formation of the Na2WO4-TiO2/SiO2 catalyst was found under test conditions of a N2/(4CH4:1O2) feed gas ratio of 1:1, a reactor temperature of 700 ºC, and gas hourly space velocity of 9,500 h −1 , exhibiting 71.7% C2+ selectivity, 6.8% CH4 conversion, and 4.9% C2+ yield. Moreover, the activity of the catalyst had good stability over 24 h of on-stream testing. The characterizations of the Na2WO4-TiO2/SiO2 catalyst using XRD, FT-IR, XPS, FE-SEM, and TEM revealed that a crystalline structure of α-cristobalite of SiO2 was present along with TiO2 crystals, substantially enhancing the activity of the catalyst for OCM reaction to C2+.

Synthesis of Value-Added Chemicals via Oxidative Coupling of Methanes over Na2WO4–TiO2–MnOx/SiO2 Catalysts with Alkali or Alkali Earth Oxide Additives

“…The weight percentage of each component on the SiO 2 support (amorphous fume silica, surface area of 85−115 m 2 g −1 ) was determined on the basis of the denoted component/element (see Table S8 and the description of Table S8 in detail). Our previous report found the optimized ratio of Na 2 WO 4 /TiO 2 /SiO 2 at 5:5:90 by wt %, 66 and in some earlier papers, 0.5−3.0 wt % of Mn in Na 2 WO 4 −MnO x −SiO 2containing catalysts was reported as promising. 54 Hence, for this study of the Na 2 WO 4 −TiO 2 −MnO x /SiO 2 catalysts with alkali or alkali earth oxide additives, catalysts consisting of 5 wt % Na 2 WO 4 , 5 wt % Ti, 0.5 wt % Mn, and 0.5 wt % X [X = no added (none), Li, K, Rb, Cs, Mg, Ca, Sr, or Cs] were employed.…”