Helping "Double Carbon" Chinese scientists achieve the best international level of low-carbon olefin yield

Beijing, May 5 (Reporter Sun Zifa) The reporter learned from the Chinese Academy of Sciences on the 19th that the scientific research team of the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences (Dalian Institute of Chemical Biology, Chinese Academy of Sciences) continued to carry out in-depth research and a large number of experiments on the basis of the creation of an oxide-molecular sieve bifunctional catalyst system (OXZEO) in 19, which created a new way of coal conversion with low water consumption and low emissions in principle, and cooperated with enterprises to carry out industrial experiments. Recently, it has successfully cracked the "seesaw" effect, which is difficult to achieve in the intertwining of conversion and selectivity in catalytic reactions, and achieved the current international best level of low-carbon olefin yield of 2016%.

This important research result paper to help ensure energy, resource security and achieve the goal of "carbon peaking and carbon neutrality" was published online in the internationally renowned academic journal Science in the early morning of May 5, Beijing time.

High-throughput fixed-bed heterogeneous catalytic reaction system catalyst loading operation. Photo courtesy of Dalian Institute of Chemicals, Chinese Academy of Sciences

According to the Dalian Institute of Chemical Sciences of the Chinese Academy of Sciences, more than 85% of the processes in the chemical industry rely on catalysts to accelerate the reaction rate. But in most cases, the two important parameters that determine the efficiency of the catalytic reaction, the conversion rate of the reactant and the selectivity of the target product, are often entangled with each other, like a "seesaw", the conversion rate increases, the selectivity decreases, and the trade-off cannot be taken into account at the same time. How to unravel this "entanglement", crack the "seesaw" effect, and achieve more accurate and efficient catalysis is an important challenge in basic science and applied research of catalysis, and it is also the direction that catalysis researchers have been working towards.

Dr. Jiao Feng, researcher Pan Xiulian and academician Bao Xinhe of the Dalian Institute of Chemistry, Chinese Academy of Sciences, found that on traditional metal or metal carbide catalysts, the activation of reactants carbon monoxide and hydrogen molecules and the formation of low-carbon olefins (including ethylene, propylene, butene) occur on the same catalytic activity center on the open catalyst surface. After a lot of research, the research team created a catalytic system of oxide and molecular sieve composite separation by active center, and successfully realized the effective separation of reactant activation and product generation two active centers, and when the carbon monoxide conversion rate was 17% for the first time in the world, the selectivity of low-carbon olefins was as high as 80%, thus breaking through the theoretical limit of 58% that the selectivity of classical Fischer-Tropsch synthesis of low-carbon hydrocarbons was difficult to surpass in a hundred years. This process eliminates the need for water gas transformation and synthesis of intermediate products, and in principle opens up a new way of converting coal with low water consumption and low emissions.

After this important breakthrough paper was published in Science in 2016, it attracted widespread attention from Chinese and foreign counterparts, and the Dalian Institute of Chemicals of the Chinese Academy of Sciences immediately cooperated with relevant enterprises to create an oxide-molecular sieve bifunctional catalyst, and completed an industrial test with an annual output of 2020,1000 tons of low-carbon olefins in 20 to verify the correctness of the scientific principle and the feasibility of the process. According to statistics, more than <> research teams at home and abroad have carried out systematic research based on this concept, and the research system has expanded from syngas conversion to efficient utilization of carbon dioxide.

On this basis, in order to further recognize and understand the innovative reaction mechanism and improve its catalytic reaction efficiency, Pan Xiulian, Bao Xinhe and the team worked closely with the team of the University of Science and Technology of China, and found through systematic and in-depth basic research and theoretical analysis that the existing molecular sieve active center not only catalyzes the main reaction of converting intermediates into low-carbon olefins, but also catalyzes the side reaction of overhydrogenation of low-carbon olefins to generate low-value alkanes or over-polymerization into macromolecular olefins, so this common active center is like a "seesaw" The fulcrum is the same, the conversion rate increases at one end, and the selectivity at the other end decreases, and the conversion rate and selectivity cannot be increased at the same time, resulting in the low carbon olefin yield cannot be improved. The experimental results of the research team show that accelerating the transport and conversion of intermediates while reducing the occurrence of side reactions in the molecular sieve pores is an effective way to unravel this entangled "seesaw" effect.

The innovative bifunctional catalyst breaks the active-selective "seesaw" in the synthesis gas to olefin reaction of coal. Photo courtesy of Dalian Institute of Chemicals, Chinese Academy of Sciences

In this study, through a large number of experiments, the research team creatively developed a microporous molecular sieve (GeAPO-18) replaced by metal germanium ion homocrystalline, which maximizes the pulling ability of molecular sieve pores to active intermediates, promotes the formation rate of intermediates, appropriately reduces its acid strength, reduces excessive hydrogenation and excessive polymerization in the process of carbon-carbon coupling, so as to reduce the occurrence of side reactions and improve the catalytic reaction performance in a two-pronged manner. In this way, the conversion and selective "seesaw" that was originally set at both ends of a fulcrum is turned into a "wing" that touches two separate active positions and can soar freely. Under the optimized reaction conditions, the single-pass conversion rate of carbon monoxide reaches 80% under the condition of maintaining the selectivity of low-carbon olefins greater than 83% (up to 85%), and achieves the current international best level of 48% low-carbon olefin yield, more than double that of the first generation catalyst.

Researcher Pan Xiulian pointed out that this concept of optimizing the transport and reaction kinetics of reaction intermediates through the separation of active centers, as well as the regulation of molecular sieve pore channels and acid site density and structural characteristics, and breaking the "seesaw" effect of conversion rate and selective entanglement in catalytic reactions, should have universal applicability to similar bifunctional catalytic systems, and will surely promote the further development of the field of zeolite catalysis research on the basis. In the next step, the research team will strive to develop a new generation of oxide-zeolite bifunctional catalysts for industrial processes to accelerate the process of industrial application.

Academician Bao Xinhe proposed higher goals, saying that in the future, it will be further combined with green hydrogen produced from renewable energy to develop China's original new coal chemical system with low water consumption and low carbon emissions, so as to help ensure the realization of the country's energy, resource security and "dual carbon" goals. (End)