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

The oxide-zeolite (OXZEO) catalyst design concept has been demonstrated in an increasing number of studies as an alternative avenue for direct syngas conversion to light olefins. We report that face-centered cubic (FCC) MnGaO_x -Spinel gives 40 % CO conversion, 81 % light olefins selectivity, and a 0.17 g g_cat ^-1  h^-1 space-time yield of light olefins in combination with SAPO-18. In comparison, solid solution MnGaO_x (characterized by Mn-doped hexagonal close-packed (HCP) Ga₂ O₃ ) 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) calculations indicate that the superior activity of MnGaO_x -Spinel can be attributed to its higher reducibility (higher concentration of oxygen vacancies) and the presence of coordinatively unsaturated Ga³⁺ sites, which facilitates the dissociation of the C-O bond via a more efficient ketene-acetate pathway to light olefins.