Surface Self-Cleaning Effect of Bifunctional Catalyst To Boost the High Yield Production of Aromatics Directly from Syngas
Direct synthesis of aromatics from syngas (STA) over an oxide–zeolite bifunctional catalyst is promising as a petroleum alternative route. Aromatics space-time yield (STY) is a key parameter for measuring the production capacity in an industrial process. However, it is still a great challenge to achieve high aromatics STY for industrial applications. Herein, we synthesized a series of CeMnOx catalysts with a self-cleaning effect. The structures and reduction process of CeMnOx catalysts were thoroughly characterized by X-ray absorption fine structure and in situ X-ray diffraction. Changes in surface carbon species during the reaction are revealed by in situ X-ray photoelectron spectroscopy and in situ Raman spectroscopy. Our results demonstrate that the intermediates can be converted to long-chain hydrocarbon or even graphite carbon species which can cover the surface of MnOx, inhibiting the reactants from further interacting with the active sites. Ce promotion in MnOx may remove the dissociated carbon species from the oxide surface by converting excess surface carbon species into short-chain hydrocarbons; thus, the growth of graphite carbon species is inhibited. This self-cleaning effect of CeMnOx catalysts facilitates the syngas conversion via maintaining a high exposure of active sites during the reaction, especially under high pressure and temperature. The aromatics STY (on carbon base) can reach as high as 4.27 mmol g–1 h–1 over CeMnOx+HZSM-5 bifunctional catalyst, which outperforms the data previously reported.
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