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

Abstract

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 À 1 h À 1 spacetime yield of light olefins in combination with SAPO-18. In comparison, solid solution MnGaO x (characterized by Mn-doped hexagonal close-packed (HCP) Ga 2 O 3 ) 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 Ga 3 + sites, which facilitates the dissociation of the CÀ O bond via a more efficient ketene-acetate pathway to light olefins.

Unraveling the Roles of Individual Metals in Bifunctional Catalysts ZnxCryMnz/SAPO-34 for Boosting Syngas Conversion to Light Olefins

“…We summed the signals in the reaction temperature range of 395–410 °C (Figure d), in which the oxygenated species of HCOOH and CH 3 OH as well as undesired CO 2 byproducts and the hydrocarbon species of CH 4 and C 3 H 6 were detected. In agreement with the results of in situ DRIFT spectroscopy (Figure a–c), the existence of HCOOH and CH 3 OH oxygenated products further demonstrated that surface active H* was involved in CO activation and the intermediates of HCOO* and CH 3 O* were formed on the surface of Zn 0.10 Cr 0.36 Mn 0.54 oxide …”

“…12,18 Furthermore, Bao et al found when the spinel structure of MnGa 2 O 4 was produced, with more oxygen vacancy sites generated, even higher CO conversion efficiency up to 40% could be achieved. 21 Therefore, deeply understanding the synergistic interactions between catalytic metals and thereby screening the doping metals are of great significance to achieve a high yield of C 2 −C 4 olefins.…”

“…Therefore, simultaneous enhancements of the conversion efficiency and the selectivity of the STO remain great challenges. Metal doping has been recognized as a promising way to increase its catalytic activity. − Li et al revealed that by doping Ga into MnO x , MnGaO x /SAPO-34 can increase the CO conversion efficiency from 8.5% to 13.7% through enhanced catalytic activity of H 2 dissociation. , Furthermore, Bao et al found when the spinel structure of MnGa 2 O 4 was produced, with more oxygen vacancy sites generated, even higher CO conversion efficiency up to 40% could be achieved . Therefore, deeply understanding the synergistic interactions between catalytic metals and thereby screening the doping metals are of great significance to achieve a high yield of C 2 –C 4 olefins.…”