【Frontiers in HaiChuan Chemical Technology】Tsinghua University team makes new progress in the research of producing olefins from syngas

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The Tsinghua University team has made new progress in the field of synthesizing olefins from syngas. The technology for directly producing olefins from syngas represents a new catalytic approach that has emerged internationally in recent years; it aims to integrate functions such as converting syngas into methanol and then methanol into olefins, thereby shortening the production process, reducing investment costs, and minimizing material and energy consumption. This technology is of great significance for the high-quality development of modern coal chemical industry in China. Since 2022, the National Development and Reform Commission and the Ministry of Industry and Information Technology have issued multiple documents advocating for its vigorous development. Typically, olefin synthesis requires an H₂/CO (hydrogen-to-carbon ratio) of >2 in the feedstock, resulting in high CO₂ emissions from coal-based syngas in the water-gas shift stage. Furthermore, the hydrogen and oxygen elements in the raw materials largely form water, which is equivalent to turning the most expensive component of the raw materials (hydrogen) into wastewater. Recently, the team led by Qian Weizhong and Cui Chaojie from the Department of Chemical Engineering at Tsinghua University reported a sodium-modified FeCx@Fe3O4 core-shell catalyst that addresses the need for high process conversion rates, high product yields, and low emissions. Overcoming the drawback of traditional catalysts being easily oxidized by water and thus becoming ineffective, this catalyst integrates the functions of water-gas shift reaction and synthesis gas to olefins production at the microscale interface. By utilizing the former to convert the water generated during the process into hydrogen in situ for the synthesis of olefins, the hydrogen atom economy of the target product is increased to 66%–86%, while the adverse effect of water on the excessive oxidation of the catalyst is significantly suppressed. The general rule for this process is that the lower the hydrogen-to-carbon ratio of the raw material (between 1 and 3), the higher the hydrogen atom economy. These values far exceed the theoretical hydrogen atom economy (50%) and actual values (43%~47%) of the conventional water-gas shift-methanol synthesis-methanol to olefins route. The team confirmed this coupling mechanism through isotope tracing and experiments to block the water-gas shift pathway, and quantitatively determined the contribution of the water-gas shift reaction on the catalyst. This provided a basis for the rational design of such catalysts. Moreover, the experiments to block the water-gas shift pathway demonstrated that the probability of CO₂ formation via the route of producing olefins from syngas is very low. The research team demonstrated that a higher hydrogen atom economy is closely related to the compatibility between the two functions of the catalyst. The water-gas shift reaction can be initiated at low temperatures, whereas the activity for olefin production depends on higher reaction temperatures. Under reaction conditions of 350°C and 2 MPa, using a feedstock with a hydrogen-to-carbon ratio of 1.5, the one-pass conversion of CO is approximately 95%, the olefin selectivity exceeds 75% (based on hydrocarbon products), and the hydrocarbon yield reaches 33 wt% (based on the feedstock). After 500 hours of continuous reaction testing, the catalyst maintained stable performance. Thanks to breakthroughs in improving the hydrogen atom economy of syngas conversion, this catalyst enables the associated water-gas shift-syngas-to-olefins route to reduce total steam consumption, total wastewater generation, and total CO₂ emissions compared with the conventional water-gas shift-methanol synthesis-methanol-to-olefins route, resulting in a 46% reduction in all environmental factors. The team is working on scaling up this technology on a pilot scale, in an effort to provide an alternative to existing coal-based olefin production methods. At the same time, thanks to its ability to make efficient use of hydrogen as a raw material, this technology may also advance research on routes for producing olefins using syngas derived from renewable electricity-driven green hydrogen (which is expensive) and new raw materials obtained by electrolyzing CO2. The research findings, titled “Conversion of syngas into olefins with high hydrogen atom economy,” were published online in Science on October 30. Gao Chang, a doctoral student in the Department of Chemical Engineering at Tsinghua University from the class of 2022, Song Wenlong, who graduated as a doctoral student in 2022, and Wang Huiqiu, who graduated as a doctoral student in 2023, are the co-first authors of the paper. Qian Weizhong, a professor in the Department of Chemical Engineering at Tsinghua University, and Cui Chaojie, an assistant researcher, are the co-corresponding authors of the paper. The research was supported by projects such as the Key R&D Program, Inner Mongolia Science and Technology Support Program, Ordos City Science and Technology ‘Breakthrough’ Project, and the Incentive Program for Advanced Manufacturing Clusters in Inner Mongolia Autonomous Region.