Su Dangsheng, Zhang Jian, and Dr. Wang Rui, Research Fellow of the Department of Catalysis Materials, Shenyang Materials Science National (Joint) Laboratory, collaborated with the German Fritz Haber Institute, the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, and the Croatian researchers to use the height on the nanodiamond surface. The bent oxygen-doped graphene active structure achieves the direct dehydrogenation of ethylbenzene to styrene under the conditions of oxygen-free and vapor-free protection, and its catalytic activity is approximately 3 times that of industrial iron oxide catalysts. No carbon deposition is generated and the surface of the nano-diamond catalyst is kept clean, which has a good application prospect in the ethylbenzene dehydrogenation industrial field. Recently, this research result was published online in the form of a newsletter on the "German Applied Chemistry", an international academic journal.
According to reports, styrene is an important basic organic raw material for the production of plastics and synthetic rubber. The catalytic dehydrogenation of ethylbenzene is currently the main method for industrial production of styrene at home and abroad.
From the process of direct dehydrogenation of alkanes, the catalysts used in industry use metals and their oxides as active components, and the alkanes molecules of the reactants are also inevitably forming carbon deposits at the same time of activation. As the reaction proceeds, the specific surface area of ​​the catalyst and pores The volume and number of active centers will gradually decrease, eventually leading to loss of catalyst activity. Therefore, carbon deposition has been a key issue that has plagued the industrial production of alkane conversion. The traditional method is to add additives such as alkali metals and rare earth metal oxides to delay the deactivation process properly, or to introduce a large amount of water vapor to carry out in-situ carbon elimination to protect the active center, which leads to a large increase in energy consumption and is economically unreasonable. With the increasing exhaustion of fossil resources and the improvement of environmental protection awareness, there is an urgent need to develop a new generation of energy-efficient, clean and highly efficient paraffin dehydrogenation catalytic materials.
Nano-carbon materials are generally produced by vapor deposition, arc discharge, laser ablation and other intense processes, containing a large number of structural defects such as voids, interstitial atoms, line defects, and boundaries. In addition, when the size of a certain dimension of the graphite structure is as small as a few nanometers, bending occurs naturally to achieve structural stability, resulting in the localized distribution of free electrons within the graphite layer, thereby increasing the chemical activity of some structural defects. After a simple surface modification, the nanocarbon surface will be modified with saturated and unsaturated functional groups containing oxygen, nitrogen and other heteroatoms, and thus have certain acid-base properties and redox ability.
The researchers found that the carbon atoms of nanodiamonds are not completely sp3 hybridized, and the surface carbon atoms undergo partial graphitization under the action of larger surface curvature, forming a unique "diamond-graphene" core-shell nanostructure. The researchers further investigated the chemical composition of surface graphene structures using synchrotron X-ray photoelectron spectroscopy and found that the oxygen atom content was as high as 5.2% at 300°C, mainly saturated oxygen species (CO) and unsaturated ketone carbonyl oxygen species ( C=O), the latter is stable even at 500°C.
This research work was conducted under the conditions of direct dehydrogenation of ethylbenzene without water vapor protection. The activity and stability of nanodiamonds and typical industrial iron oxide catalysts were investigated. The results showed that the conversion rate on the iron oxide catalyst rapidly decreased from 20.2% to 7.1% after 5 hours from the start of the reaction, while the conversion rate on the nanodiamond was higher than 20.5% in 120 hours and the styrene selectivity was as high as 97.3%. After the reaction, serious carbon deposition occurred on the iron oxide, and its active surface was covered with disordered carbon, while the surface structure of the nano-diamond did not change significantly. The researchers used in-situ FT-IR spectroscopy and in situ near-infrared X-ray photoelectron spectroscopy to further investigate the non-metal catalytic mechanism and the reasons for reduced activity during the induction period, directly verifying the direct dehydrogenation of unsaturated ketone carbonyl oxygen species. A decisive role. The benzene ring structure in the ethylbenzene molecule does not adsorb, and the hydrogen atoms of the CH bond in the saturated branch chain are adsorbed on the ketone carbonyl oxygen, and a certain number of substituted aromatic alcohol transition intermediate structures are formed. During the induction period of the reaction, the ketone carbonyl oxygen species are gradually saturated with hydrogen atoms. The decrease in the number of active sites leads to a 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 research uses non-metal materials for the direct dehydrogenation reaction, and uses advanced in-situ characterization techniques to make important breakthroughs in non-metallic catalytic reaction mechanisms, active-site structures, and reaction intermediates and other key scientific issues. The direction of in-depth development and ethylbenzene dehydrogenation of the traditional industry technology upgrade provides an important reference. The study received some support from the Institute for the Introduction of Excellent Scholars at the Metal Research Institute and the Innovation Project of the National Natural Science and Technology Committee.