OX-Zeo Bifunctional Catalyst Concept Enables Syngas Conversion to Light Olefins and Beyond

Title：

OX-ZEO bifunctional catalyst concept enables syngas conversion to light olefins and beyond

Authors:

Feng Jiao, XiulianPan,* Junhao Yang, Gen Li, Na Li, Yuxiang Chen, Xinhe Bao*

State Key Laboratory of Catalysis and Dalian National Laboratory for Clean Energy Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, China.

*Xiulian Pan: panxl@dicp.ac.cn; *Xinhe Bao: xhbao@dicp.ac.cn

Abstract text

Light olefins, include ethylene, propylene and butylene, are important chemical building blocks which are widely used for producing plastics, cosmetics, and drugs. Syngas, as a platform of coal, natural gas and biomass utilization, can be transformed to light olefins via traditional Fischer-Tropsch synthesis (FTS).¹ However, hydrocarbon distributions of FTS follows the so-called Anderson-Schulz-Flory (ASF) distribution, according to which the selectivity of C₂-C₄ hydrocarbon does not exceed 58%.^1-3 Therefore, to precisely control the C-C coupling as well as suppress the methane formation and over-hydrogenation of olefins are key challenges in this filed.

We recently reported a bifunctional catalyst design concept of OX-ZEO (Oxide-Zeolite) for syngas conversion. For example, a mix of ZnCrO_x metal oxides and mesopore SAPO-34 (MSAPO) leads to a light olefin selectivity up to 80% in hydrocarbons at CO conversion of 17%.⁴ This selectivity is much higher than the upper limit of C₂-C₄ according to the ASF model and the best iron and cobalt based FTS catalysts reported so far. We demonstrated that this OX-ZEO concept turns syngas conversion into a tandem reaction, i.e. activating CO and H₂, generating intermediates over the partially reduced metal oxides, and C-C coupling within the pores of zeolites.⁴ Thus, the product selectivity can be manipulated with shape-selective zeolites by changing the acidity and topology of zeolites.^4-6 In addition, it is important to match the two components properly in terms of the compositions, structures and intimacy to achieve an optimum catalytic activity and selectivity. This concept is further corroborated by substituting the zeolite component with mordenite, which steers syngas conversion selectively toward ethylene. The selectivity of ethylene alone in hydrocarbons reaches as high as 83%.⁶ If the zeolite component is ZSM-5, syngas then can be selectively converted to aromatics and the selectivity reaches 73%.⁵ Furthermore, our recent results shown that this concept can be extended for direct synthesis of liquid fuels and oxygenates from syngas. In addition, it was demonstrated recently that this concept is also applicable to CO₂ hydrogenation to form a variety of chemicals.^7-10 Although the mechanisms how the two functionalities cooperate and how the product selectivity is controlled are not well understood yet, the increasing number of publications in CO and CO₂ hydrogenation^4-14 reveals the versatility of this concept and may provide a third alternative for fabrication of basic chemicals from non-petroleum carbon resources such as coal, natural gas and biomass. In this presentation, detailed discussion will be given about the OX-ZEO catalyst design concept and the possible reaction mechanism.

References

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