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Does in-situ-generated H2O2 promote important industrial reactions?

2022; Elsevier BV; Volume: 8; Issue: 6 Linguagem: Inglês

10.1016/j.chempr.2022.05.006

2451-9308

Linfang Lu, Baizeng Fang,

Electrochemical Analysis and Applications

Recently in Science, Hutchings and co-workers reported an efficient TS-1-supported AuPd alloy nanoparticle catalyst that produced cyclohexanone oxime with a selectivity > 95% through the in-situ-generated H2O2, comparable to the current industrial route. The use of in-situ-generated H2O2 can achieve great cost savings in current industrial production of oxime and is believed to have bright prospects in other industrial chemical reactions that need H2O2. Recently in Science, Hutchings and co-workers reported an efficient TS-1-supported AuPd alloy nanoparticle catalyst that produced cyclohexanone oxime with a selectivity > 95% through the in-situ-generated H2O2, comparable to the current industrial route. The use of in-situ-generated H2O2 can achieve great cost savings in current industrial production of oxime and is believed to have bright prospects in other industrial chemical reactions that need H2O2. As a mild and environmentally friendly oxidant, H2O2 has been widely used in industry for green chemical synthesis. At present, H2O2 used in chemical reactions often needs to be prepared in advance by heterogeneous catalysis.1Shi X. Back S. Gill T.M. Siahrostami S. Zheng X. Electrochemical synthesis of H2O2 by two-electron water oxidation reaction.Chem. 2021; 7: 38-63Abstract Full Text Full Text PDF Scopus (91) Google Scholar However, all industrial chemical transformations that use preformed H2O2 inevitably suffer from economic and environmental losses due to the low stability of H2O2.2Chu L. Cang L. Fang G. Sun Z. Wang X. Zhou D. Gao J. A novel electrokinetic remediation with in-situ generation of H2O2 for soil PAHs removal.J. Hazard Mater. 2022; 428: 128273Crossref PubMed Scopus (10) Google Scholar The ammoximation of cyclohexanone to produce cyclohexanone oxime is an important industrial reaction because cyclohexanone oxime is a key precursor to caprolactam, a commodity chemical used in the synthesis of polyamide nylon-6.3Lorenzo D. Romero A. Del-Arco L. Santos A. Linear amides in caprolactam from linear ketone impurities in cyclohexanone obtained from cyclohexane: Kinetics and identification.Ind. Eng. Chem. Res. 2019; 58: 11878-11890Crossref Scopus (6) Google Scholar The important process of realizing this reaction in current industry is using titanium silicate-1 (TS-1) as the catalyst and cyclohexanone, ammonia, and preformed H2O2 as the reactants.4Ding W. Peng H. Zhong W. Mao L. Yin D. Site-specific catalytic activities to facilitate solvent-free aerobic oxidation of cyclohexylamine to cyclohexanone oxime over highly efficient Nb-modified SBA-15 catalysts.Catal. Sci. Technol. 2020; 10: 3409-3422Crossref Google Scholar The hydroxylamine could be generated on the TS-1 catalyst from ammonia oxidized by H2O2 and then react with cyclohexanone non-catalytically to produce cyclohexanone oxime. Obviously, the use of preformed H2O2 in this reaction greatly increases the cost of producing cyclohexanone oxime. Recently in Science, Hutchings and co-workers innovatively developed an efficient TS-1-supported AuPd alloy nanoparticle catalyst to generate H2O2 in situ on AuPd nanoparticles, acquiring cyclohexanone oxime with a selectivity > 95%, comparable to the current industrial route.5Lewis R.J. Ueura K. Liu X. Fukuta Y. Davies T.E. Morgan D.J. Chen L. Qi J. Singleton J. Edward J.K. et al.Highly efficient catalytic production of oximes from ketones using in situ–generated H2O2.Science. 2022; 376: 615-620Crossref PubMed Scopus (26) Google Scholar By optimizing the reaction conditions, the authors could connect the direct synthesis of H2O2 with the ammoximation of cyclohexanone to produce cyclohexanone oxime with high yields (Figure 1A). The alloying of Au with Pd was critical to realizing a high yield of cyclohexanone oxime (77% oxime yield) by using a supported 0.33%Au-0.33%Pd/TiO2(chloride-O) catalyst in conjunction with commercial TS-1 (Figure 1B). With this catalyst, high oxime selectivities (all > 95%) can be achieved with a range of other ketones (Figure 1C), indicating the universality of the in situ approach to producing oxime. Meeting the industrial application requires a composite catalyst that can both synthesize H2O2 and catalyze the formation of hydroxylamine instead of a co-catalyst system (i.e., the physical mixture of supported catalyst with TS-1). Therefore, the authors synthesized the composite catalyst (0.33%Au-0.33%Pd/TS-1(chloride-O)). Although the oxime yield (43%) with this composite catalyst was lower than that (77%) with the co-catalyst (i.e., 0.33%Au-0.33%Pd/TiO2(chloride-O) catalyst in conjunction with TS-1), it is possible to enhance the oxime yield by varying the Pd precursor and calcination condition when preparing the composite catalyst. The oxime yield was increased considerably to 79% with the use of this new composite catalyst (i.e., 0.33%Au-0.33%Pd/TS-1(acetate-O+R)) (Figure 1D). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and elemental mapping showed that larger (5–20 nm) AuPd alloy nanoparticles mainly anchored on the minority TiO2 phase and that smaller (1–3 nm) Pd-only particles deposited on the minority TiO2 phase or majority TS-1 phase (Figure 1E). The stability test indicated that the oxime yield of the catalyst was retained (≥80%) after three consecutive ammoximation reactions. It is interesting to note that the dispersion and composition of the AuPd alloy nanoparticles on the minority TiO2 phase were basically maintained after three cycles (Figure 1F). In combination with the systematic control experiments presented in the paper, it can be concluded that the AuPd alloy nanoparticles loaded on the TiO2 minority component of the TS-1 are key to obtaining high catalytic activity. To further verify the stability and potential industrial application of the 0.33%Au-0.33%Pd/TS-1(acetate-O+R) catalyst, Hutchings and co-workers designed a continuous-flow reactor with cyclohexanone and ammonia concentrations identical to those applied in the industrial ammoximation process. Interestingly, the cyclohexanone oxime yield and H2 selectivity stabilized at 48% and 70%, respectively, after several hours, and there was slight catalytic activity loss after 40 h of reaction (Figure 1G). Further investigations showed that the cyclohexanone oxime yield could be enhanced through the optimization of the reaction conditions (87%). This work is so excellent that we have seen the possibility of using in-situ-generated H2O2 to alter an important industrial reaction. In fact, it has been a long-standing goal to use in-situ-generated H2O2 for chemical transformations. Earlier studies tried to apply it to some selective oxidation reactions, such as alcohol oxidation6Crombie C.M. Lewis R.J. Taylor R.L. Morgan D.J. Davies T.E. Folli A. Murphy D.M. Edwards J.K. Qi J. Jiang H. et al.Enhanced selective oxidation of benzyl alcohol via in situ H2O2 production over supported Pd-based catalysts.ACS Catal. 2021; 11: 2701-2714Crossref Scopus (58) Google Scholar and the partial oxidation of methane.7Jin Z. Wang L. Zuidema E. Mondal K. Zhang M. Zhang J. Wang C. Meng X. Yang H. Mesters C. et al.Hydrophobic zeolite modification for in situ peroxide formation in methane oxidation to methanol.Science. 2020; 367: 193-197Crossref PubMed Scopus (323) Google Scholar Nevertheless, these works have not demonstrated that the in situ approach can replace the current industrial processes, mainly because of the low conversion rates or poor selectivity toward desired products. This is the first report showing that it is possible to connect the direct synthesis of H2O2 with an important industrial reaction to produce desired products with high yields. The use of in-situ-generated H2O2 can achieve great cost savings in the current industrial production of oxime. Although this work has taken a big step forward, some issues still need to be addressed. First, the catalyst lifetime should be extended. The authors conducted a detailed technoeconomic evaluation between the in situ approach and the current industrial process toward the ammoximation of cyclohexanone to produce cyclohexanone oxime. The in situ approach with 0.33%Au-0.33%Pd/TS-1(acetate-O+R) catalyst saved 13% in material costs alone when the catalyst lifetime was 2.3 years. However, the stability test was limited to 248 h, which needs to be extended significantly. Second, the reaction should be scaled up. Although the designed continuous-flow reactor kept the concentrations of cyclohexanone and ammonia identical to those applied in the industrial ammoximation process, some chemical engineering problems (e.g., safety issues and catalyst carbon deposition) arose when it came to industrial scale-up. There is no doubt that this work is a breakthrough in the chemical scientific world. We believe that in-situ-generated H2O2 promotes some important industrial reactions, and further research direction should focus on connecting the direct synthesis of H2O2 with these industrial reactions. This work was supported by the Zhejiang Provincial Natural Science Foundation of China (LQ20B030011) and the startup fund of Hangzhou Normal University (2019QDL001). The authors declare no competing interests.