Oxidative coupling of methane—comparisons of MnTiO(3)–Na(2)WO(4) and MnO(x)–TiO(2)–Na(2)WO(4) catalysts on different silica supports

The oxidative coupling of methane (OCM) converts CH(4) to value-added chemicals (C(2+)), such as olefins and paraffin. For a series of MnTiO(3)-Na(2)WO(4) (MnTiO(3)-NW) and MnO(x)-TiO(2)-Na(2)WO(4) (Mn-Ti-NW), the effect of loading of MnTiO(3) or MnO(x)-TiO(2), respectively, on two different supports (sol–gel SiO(2) (SG) and commercial fumed SiO(2) (CS)) was examined. The catalyst with the highest C(2+) yield (21.6% with 60.8% C(2+) selectivity and 35.6% CH(4) conversion) was 10 wt% MnTiO(3)-NW/SG with an olefins/paraffin ratio of 2.2. The catalyst surfaces with low oxygen-binding energies were associated with high CH(4) conversion. Stability tests conducted for over 24 h revealed that SG-supported catalysts were more durable than those on CS because the active phase (especially Na(2)WO(4)) was more stable in SG than in CS. With the use of SG, the activity of MnTiO(3)-NW was not substantially different from that of Mn-Ti-NW, especially at high metal loading.