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₊.