| Hydrogen peroxide is a kind of efficient green chemical product that is widely used in advanced oxidation technology such as waste water treatment,gas scrubbing,and disinfection due to its strong oxidation,safety and easy accessibility.Due to the wide application of hydrogen peroxide in the field of environmental treatment,and the increasing demand for hydrogen peroxide year by year,however,the common industrial method to produce hydrogen peroxide,i.e.Anthraquinone process,suffers from the massive energy consumption and side products which are harmful to the environment.In recent years,the direct synthesis of hydrogen peroxide from water and oxygen with suitable catalysts is a promising synthetic method which has the advantages of relatively simple process,high atomic economy and environmental friendliness.The mixture of hydrogen and oxygen will have the possibility of explosion.Therefore,this article replaces hydrogen with water as the raw material for the reaction based on the direct synthesis of hydrogen peroxide from hydrogen and oxygen.In this paper,density functional theory is used to study the constructed carbon nanotubes or graphene supported zero-valent Al,Zn,Fe metal single-atom catalysts.Oxygen and water were used as reaction materials to catalyze hydrogen peroxide preparation.By comparing the adsorption energy of different positions of metals on the surface of carbon nanotubes and graphene,the optimal adsorption sites were determined,and a stable catalyst model was selected.At the same time,two different reaction paths for the synthesis of hydrogen peroxide and a side reaction path that may generate hydrogen were proposed in this paper,and the microscopic reaction mechanisms of the catalyst catalyzing water and oxygen to synthesize hydrogen peroxide were studied respectively.In this paper,Materials Studio 7.0 software was used to optimize the stable structure of reactants,intermediates and products in each path.The LST/QST method is employed to search the transition states of the reactions and correctness of the optimized transition state structures are verified by the frequency analysis.Finally,by comparing the activation energy of different reaction paths,the optimal reaction path was obtained,and the possibility of side reaction products was predicted.By comparing the reaction energy barriers of the control steps of the three paths,we found that activation energy of catalyst R(Al,Zn,Fe)-SWCNT and R(Al,Zn,Fe)-GR under aerobic conditions for synthesis hydrogen peroxide is not high,which indicates that carbon-supported three metals(Al,Zn,Fe)catalysts can be directly used for oxygen and water as raw materials to synthesize hydrogen peroxide,and side effects to generate hydrogen can hardly take place.At the same time,through comparing the energy barriers of the series of R-GR and R-SWCNT,it can be seen that in addition to metal Fe,the energy barrier of the optimal route for the catalyst R(Al,Zn)-GR to catalyze the synthesis of hydrogen peroxide Catalyst R(Al,Zn)-SWCNT is lower.However,the energy barriers of the side reaction pathways that generate hydrogen are all increased.This indicates that R-GR is more likely to catalyze the generation of hydrogen peroxide,and its by-product reaction is less likely to occur,so it is a better catalyst choice.In addition,this paper also studied the electron density,band structure and density of states characteristics of various catalysts,and analyzed the correlation between the physical properties of the catalysts and their catalytic performance.Our research results well explain the experimental phenomenon of Zn-SWCNT based catalysis to produce hydrogen peroxide,and we found that the metal loaded on graphene has better catalytic performance,and then we also predict that catalysts of carbon supporting metal Al and Fe may have the same catalytic ability.We hope that our present work can provide valuable theoretical information for the optimization of catalyst and the direct application of hydrogen peroxide in hydrogen peroxide industry. |
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