Tuning the Crystal Phase to Form MnGaOx-Spinel for Highly Efficient Syngas to Light Olefins.

Oxide-Zeolite (OXZEO) catalyst design concept has been demonstrated in an increasing number of studies to provide an alternative avenue for direct syngas conversion to light olefins. We herein report that face centered-cubic (FCC) MnGaOx-Spinel gives 40% CO conversion, 81% light olefins selectivity, and 0.17 g·gcat-1·h-1 space-time yield of light olefins in combination with SAPO-18. In comparison, solid solution MnGaOx (characterized by Mn-doped hexagonal close-packed (HCP) Ga2O3) with a similar chemical composition gives a much inferior activity, i.e., the specific surface activity is one order of magnitude lower than the spinel oxide. Photoluminescence (PL), in situ fourier transform infrared (FT-IR), and density functional theory (DFT) calculation indicate that the superior activity of MnGaOx-Spinel can be attributed to its higher reducibility (higher concentration of oxygen vacancies) and the presence of coordinatively unsaturated Ga3+ site, which facilitates the dissociation of the C-O bond via a more efficient ketene-acetate pathway to light olefins.