New progress in the research on producing aromatics via carbon dioxide hydrogenation

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New Progress in the Research on Converting Carbon Dioxide into Aromatics via Hydrogenation Author/Source: Date: November 26, 2018 Clicks: 52 New Progress in the Research on Converting Carbon Dioxide into Aromatics via Hydrogenation Author: November 23, 2018 Source: Chinese Academy of Sciences According to Sinochem News, researchers from the Key Laboratory of Catalytic Fundamentals at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, including Academician Li Can of the Chinese Academy of Sciences, Dr. Li Zelong, and Ph.D. student Qu Yuanzhi, have made new advances in the research on using catalytic hydrogenation of CO2 to produce aromatics – enabling the direct and highly selective conversion of CO2 into aromatics through a tandem catalyst system. Recently, these research findings were published in Joule. 　　Li Can’s team has been dedicated for a long time to solar photocatalysis, photoelectrocatalysis, electrocatalytic water splitting for hydrogen production, and CO2 conversion. Using clean energy to produce hydrogen in order to convert CO2 into fuels and chemicals is an important strategy for reducing CO2 emissions and achieving sustainable utilization of carbon resources. Aromatic hydrocarbons are one of the important basic chemical raw materials in the synthesis of organic materials. Using aromatic hydrocarbons, a variety of polymer materials can be synthesized, such as polystyrene, phenol resins, nylon, and polyethylene terephthalate resins. The traditional methods for synthesizing aromatic hydrocarbons are primarily the cracking of naphtha, and the methanol-to-aromatics (MTA) route developed in recent years, both of which rely on fossil resources (oil and coal). Therefore, hydrogen produced from renewable energy is used to convert CO2 into aromatic compounds with high added value, allowing CO2 to be stored in the form of polymer materials. This approach not only enables the sustainable utilization of CO2 as a carbon resource but also helps to reduce CO2 emissions, holding significant strategic importance. However, CO2 is a thermodynamically inert molecule, and there are significant difficulties and challenges in activating CO2 and achieving highly selective transformations. 　　In this work, building on the research by Li Can’s team on the production of methanol via hydrogenation of CO2 in ZnZrO solid solutions (Science Advances 2017), as well as the study on the production of low-carbon olefins via hydrogenation of CO2 in a ZnZrO/SAPO tandem system (ACS Catal. 2017), they further developed a ZnZrO/ZSM-5 tandem catalyst system. This catalyst converts CO2 to aromatics with high selectivity through hydrogenation; when the one-pass conversion rate of CO2 is 14%, the selectivity for aromatics among the hydrocarbons reaches 73% to 78%, while the selectivity for CO can be reduced to 44%. Research has found that the key to hydrogenating CO2 into aromatics lies in the effective synergy of cascaded catalysts. Infrared spectroscopy, chemical trapping, and experiments show that CO2 and H2 are activated on ZnZrO solid solution oxides to form CHxO intermediate species, which migrate from the surface of ZnZrO into the pores of the molecular sieve, thereby enabling the formation of aromatics. The synergistic mechanism between the catalysts in series, along with the surface migration of the key intermediate species CHxO, enables the thermodynamic and kinetic coupling of CO2 hydrogenation to direct formation of aromatics. An appropriate amount of H2O generated in the CO2 hydrogenation reaction significantly promotes the aromatization of olefins by inhibiting the adsorption of low-carbon olefins on the weak acid sites of the molecular sieve. Due to the presence of H2O and CO2 in the reaction system, which creates a weakly oxidizing environment, the formation of polycyclic aromatic hydrocarbons on the catalyst is suppressed, thereby extending the catalyst’s lifespan; no significant deactivation was observed in this catalyst during 100 hours of reaction time. This technology opens up new approaches for CCO2 conversion.