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.