Researcher of the Department of Catalytic Materials, Institute of Materials Science, Chinese Academy of Sciences, Institute of Catalysis Materials, Su Fangsheng, Researcher Zhang Jian, Dr. Wang Rui, and the Fritz Haber Institute of Germany, the Changchun Institute of Chinese Academy of Sciences, and the Croatian researchers, with the help of The highly curved oxygen-doped graphene active structure on the diamond surface realizes the direct dehydrogenation of ethylbenzene to styrene under the low temperature condition of no oxygen and anhydrous steam protection, and its catalytic activity is about 3 times that of industrial iron oxide catalyst. There is no carbon deposit in the reaction process and the surface of the diamond catalyst remains clean, which has a good application prospect in the field of ethylbenzene dehydrogenation. This work was published online on October 1st at Angewandte Chemie International Edition.
Catalytic basic research is closely related to the development of modern chemical industry. About 80% of chemical products are produced directly or indirectly by catalytic processes. Industrial catalysts with excellent performance must be able to maintain good catalytic activity and selectivity for a long period of time, and have good thermal conductivity, wear resistance and regeneration properties. Taking the alkane direct dehydrogenation process as an example, the traditional catalyst uses metal and its oxide as active components, and the reactant alkane molecules inevitably form carbon deposits while activating, and the specific surface area, pore volume and number of active centers of the catalyst Will gradually decline, eventually leading to loss of catalyst activity. Carbon deposition has always been a key issue in the alkane conversion industry. The traditional method is to add alkali metal, rare earth metal oxide and other additives to delay the deactivation process, or introduce a large amount of water vapor for carbonization in situ to protect the active center. With the depletion of fossil resources and the gradual improvement of environmental protection awareness, it is urgent to develop a new generation of energy-saving, clean and efficient alkane dehydrogenation catalytic materials.
Nano-carbon materials are generally produced by violent processes such as vapor deposition, arc discharge, and laser ablation, and contain a large number of structural defects such as vacancies, interstitial atoms, line defects, and boundaries. In addition, when the size of the graphite structure is as small as a few nanometers in a certain dimension, the bending naturally occurs in order to achieve structural stability, resulting in localized distribution of free electrons in the graphite layer, thereby improving the chemical activity of some structural defects. After a simple surface modification, the surface of the nanocarbon will be modified with saturated and unsaturated functional groups containing oxygen, nitrogen and other heteroatoms, and thus have certain acid-base properties and redox capabilities.
Researcher Su Dangsheng and his collaborators found that the carbon atoms of nanodiamonds are not completely sp3 hybridized, and the surface carbon atoms are partially graphitized under the action of large surface curvature, forming a unique "diamond-graphene". Core-shell nanostructures. Further, the chemical composition of the surface graphene structure was investigated by synchrotron radiation X-ray photoelectron spectroscopy. It was found that the oxygen atom content was as high as 5.2% at 300 °C, mainly saturated ether oxygen species (C–O) and unsaturated ketone carbonyl oxygen species (C). =O), the latter can still exist stably even at 500oC. Under the direct dehydrogenation conditions of anhydrous vapor protection, the researchers investigated the activity and stability of nanodiamonds and typical industrial iron oxide catalysts. The results showed that after 5 hours from the start of the reaction, the conversion on the iron oxide catalyst was rapidly reduced from 20.2% to 7.1%, while the conversion on the nanodiamond was higher than 20.5% in 120 hours, and the styrene selectivity was as high as 97.3%. After the reaction, severe carbon deposition occurred on the iron oxide, and the active surface was surrounded by disordered carbon; while the surface structure of the nanodiamond did not change significantly. The in-situ infrared spectroscopy and in-situ near-normal pressure X-ray photoelectron spectroscopy were used to study the non-metal catalytic mechanism and the cause of the decrease in activity during the induction period, and directly verified the decisive role of unsaturated ketone carbonyl oxygen species in direct dehydrogenation. . The benzene ring structure in the ethylbenzene molecule does not adsorb, and the hydrogen atom of the C-H bond in the saturated branch is adsorbed on the ketone carbonyl oxygen and forms a certain number of substituted-substituted aromatic alcohol transition intermediate structures. During the induction period of the reaction, the ketocarbonyloxy active species are gradually saturated by hydrogen atoms, and the decrease in the number of active sites leads to partial loss of activity, and the initial activity can be restored by treating the catalyst with air at a lower temperature.
For the first time, this study used non-metallic materials to catalyze direct dehydrogenation, and advanced in-situ characterization methods to achieve important breakthroughs in key scientific issues such as non-metal catalytic reaction mechanism, active site structure and reaction intermediates. The in-depth development and technical upgrading of the traditional industry of ethylbenzene dehydrogenation provide an important reference.
Catalytic basic research is closely related to the development of modern chemical industry. About 80% of chemical products are produced directly or indirectly by catalytic processes. Industrial catalysts with excellent performance must be able to maintain good catalytic activity and selectivity for a long period of time, and have good thermal conductivity, wear resistance and regeneration properties. Taking the alkane direct dehydrogenation process as an example, the traditional catalyst uses metal and its oxide as active components, and the reactant alkane molecules inevitably form carbon deposits while activating, and the specific surface area, pore volume and number of active centers of the catalyst Will gradually decline, eventually leading to loss of catalyst activity. Carbon deposition has always been a key issue in the alkane conversion industry. The traditional method is to add alkali metal, rare earth metal oxide and other additives to delay the deactivation process, or introduce a large amount of water vapor for carbonization in situ to protect the active center. With the depletion of fossil resources and the gradual improvement of environmental protection awareness, it is urgent to develop a new generation of energy-saving, clean and efficient alkane dehydrogenation catalytic materials.
Nano-carbon materials are generally produced by violent processes such as vapor deposition, arc discharge, and laser ablation, and contain a large number of structural defects such as vacancies, interstitial atoms, line defects, and boundaries. In addition, when the size of the graphite structure is as small as a few nanometers in a certain dimension, the bending naturally occurs in order to achieve structural stability, resulting in localized distribution of free electrons in the graphite layer, thereby improving the chemical activity of some structural defects. After a simple surface modification, the surface of the nanocarbon will be modified with saturated and unsaturated functional groups containing oxygen, nitrogen and other heteroatoms, and thus have certain acid-base properties and redox capabilities.
Researcher Su Dangsheng and his collaborators found that the carbon atoms of nanodiamonds are not completely sp3 hybridized, and the surface carbon atoms are partially graphitized under the action of large surface curvature, forming a unique "diamond-graphene". Core-shell nanostructures. Further, the chemical composition of the surface graphene structure was investigated by synchrotron radiation X-ray photoelectron spectroscopy. It was found that the oxygen atom content was as high as 5.2% at 300 °C, mainly saturated ether oxygen species (C–O) and unsaturated ketone carbonyl oxygen species (C). =O), the latter can still exist stably even at 500oC. Under the direct dehydrogenation conditions of anhydrous vapor protection, the researchers investigated the activity and stability of nanodiamonds and typical industrial iron oxide catalysts. The results showed that after 5 hours from the start of the reaction, the conversion on the iron oxide catalyst was rapidly reduced from 20.2% to 7.1%, while the conversion on the nanodiamond was higher than 20.5% in 120 hours, and the styrene selectivity was as high as 97.3%. After the reaction, severe carbon deposition occurred on the iron oxide, and the active surface was surrounded by disordered carbon; while the surface structure of the nanodiamond did not change significantly. The in-situ infrared spectroscopy and in-situ near-normal pressure X-ray photoelectron spectroscopy were used to study the non-metal catalytic mechanism and the cause of the decrease in activity during the induction period, and directly verified the decisive role of unsaturated ketone carbonyl oxygen species in direct dehydrogenation. . The benzene ring structure in the ethylbenzene molecule does not adsorb, and the hydrogen atom of the C-H bond in the saturated branch is adsorbed on the ketone carbonyl oxygen and forms a certain number of substituted-substituted aromatic alcohol transition intermediate structures. During the induction period of the reaction, the ketocarbonyloxy active species are gradually saturated by hydrogen atoms, and the decrease in the number of active sites leads to partial loss of activity, and the initial activity can be restored by treating the catalyst with air at a lower temperature.
For the first time, this study used non-metallic materials to catalyze direct dehydrogenation, and advanced in-situ characterization methods to achieve important breakthroughs in key scientific issues such as non-metal catalytic reaction mechanism, active site structure and reaction intermediates. The in-depth development and technical upgrading of the traditional industry of ethylbenzene dehydrogenation provide an important reference.
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