Performance of Silicotungstic Acid Incorporated Mesoporous Catalyst in Direct Synthesis of Dimethyl Ether from Syngas in the Presence and Absence of CO₂

Dimethyl ether (DME), which is an excellent green diesel fuel alternate, is synthesized following a direct synthesis route from synthesis gas, by using a bi-functional catalyst mixture, which was composed of a silicotungstic acid incorporated mesoporous catalyst [TRC-75(L)] and a commercial Cu–Zn based catalyst. Higher DME selectivity values were obtained by using TRC-75(L), than commercial γ-alumina at 50 bars. Presence of CO₂ in the feed stream caused significant enhancement in DME selectivity. Results showed that DME selectivity of about 0.85 was obtained in a temperature range 250–275 °C in the presence of 10 % CO₂. In fact, CO₂ was also used as a resource to produce DME at lower temperatures. Reverse dry reforming and ethanol formation reactions were observed as side reactions, especially at higher temperatures. Results also proved that direct synthesis of DME from syngas has major CO conversion and DME selectivity advantages over the two step process involving consecutive methanol synthesis and dehydration steps.