Wang Yong, research team of Suzhou Research Institute, Lanzhou Institute of chemistry, Chinese Academy of Sciences: new progress has been made in the catalytic mechanism of direct synthesis of H2O2

Wang Fang: Recently, Wang Yong, a researcher at the Suzhou Research Institute of Lanzhou Institute of chemical engineering, Chinese Academy of Sciences, has worked with Professor Sam P de Visser of University of Manchester, UK, to make new progress in the catalytic mechanism of direct synthesis of H 2 O 2 The team found that oxidized PD has an important effect on the activity and selectivity of direct synthesis of H 2O 2 The related research results were published in the Journal of the American Chemical Society (J am Chem SOC., DOI: 10.1021 / JACS 8b10281) H 2O 2 is considered to be an environmentally friendly oxidant because its by-product is only H 2O It has been widely used in many industries such as textile, papermaking, food, aquaculture and wastewater treatment At present, the anthraquinone method developed by Riedl and Pfleiderer is the main method for the industrial production of H 2O 2 This method can effectively avoid the direct contact between H 2 and O 2, and has high safety It is suitable for large-scale continuous production However, there are many problems in this method, such as the complex separation steps of H 2O 2, the complex concentration steps of products before transportation and the lack of economy The direct synthesis of H 2O 2 from H 2 and O 2 is an atom economic and environment-friendly reaction, so it is considered to be one of the most potential reactions for the preparation of H 2O 2 by substituting anthraquinone method, which has been widely concerned in recent years As shown in Figure 1, H 2 reacts with O 2, and H 2O is a more favorable product in thermodynamics than H 2O 2 Even though H 2O 2 can be generated, it can easily be further converted to H 2O by decomposition or hydrogenation Therefore, how to overcome the problem of H 2O 2 selectivity is the biggest challenge for this reaction The key to solve this problem lies in the design of catalyst PD is one of the most active catalysts, but its selectivity to H 2O 2 is very poor The selectivity of Pd catalyst is often improved by alloying or adding additives However, there are different opinions on the factors affecting PD selectivity In particular, the effect of oxidized Pd on the activity and selectivity of direct synthesis of H 2 O 2 has not been studied Fig 1 The main reactions and side reactions (source: J am Chem SOC.) of H 2O 2 direct synthesis from H 2 and O 2 In this work, the researchers systematically studied the adsorption and decomposition behaviors of O 2 and H 2 of reaction substrate components by using density functional theory calculation, in which the pure PD surface represents the reduced PD and the PDO surface represents the oxidized PD ）, and the process of producing H 2O 2 and H 2O by reaction on PD and PDO surfaces (Fig 3) The results show that O 2 has a strong interaction with the surface of pure PD, only 0.7 EV is needed for decomposition, and H 2 is directly dissociated and adsorbed on the surface of pure PD On the surface of PDO, the adsorption of O 2 and H 2 is weaker than that on the surface of pure PD, and O 2 is not easy to decompose H 2 can decompose when it crosses the medium energy barrier It is generally believed that the formation of H 2O 2 consists of two elementary steps: (1) O 2 and H atoms form an ooh · intermediate; (2) ooh · intermediate grabs h to form H 2O 2 The decomposition of O 2, ooh · intermediate and H 2O 2 is easy to produce by-product H 2O, reducing the selectivity of H 2O 2 Further research shows that the path of H 2O formation is more favorable than that of H 2O 2 formation on the surface of pure PD; on the surface of PD, the path of H 2O 2 formation is dominant, and ooh · intermediate and H 2O 2 are not easy to decompose Fig 2 Adsorption and decomposition behavior of O 2 and H 2 (source: J am Chem SOC.) Fig 3 The process of O 2 and H 2 reacting on PD and PDO surfaces to generate H 2O 2 and H 2O (source: J am Chem SOC.) this paper discusses the electronic structure, geometric structure, thermodynamics and other aspects of the reduced and oxygenated PD in H 2O 2 The differences of synthesis selectivity were analyzed in detail These studies indicate that PD is more favorable for the formation and stability of H 2O 2, which is one of the most important factors to determine the selectivity of H 2O 2 It can provide a new idea for the design of catalysts The research work was greatly supported by the "special talent program" of Lanzhou Institute of chemical and physical sciences, Chinese Academy of Sciences, and the National Natural Science Foundation (218730521173211, 21203218 and 21633013).