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    Home > Research group of Professor Wang Yong of Zhejiang University: precise design of high efficiency alkynol semi hydrogenation catalyst

    Research group of Professor Wang Yong of Zhejiang University: precise design of high efficiency alkynol semi hydrogenation catalyst

    • Last Update: 2019-08-15
    • Source: Internet
    • Author: User
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    The production process of lead vitamins (including vitamin E, vitamin A, vitamin B6, etc.) involves multi-step alkynol semi hydrogenation reaction The yield of the target product enol is closely related to the economic benefits of the final product vitamin Meanwhile, the product quality of the hydrogenation process determines the market competitiveness of vitamin products to a large extent At present, Lindlar catalyst is mainly used in industry to improve selectivity at the cost of greatly sacrificing activity Its catalytic efficiency is low The use of toxic heavy metals (Pb, Bi, etc.) will also bring environmental problems In the actual production process, it is still necessary to use toxic organic auxiliaries to further improve selectivity, improve separation energy consumption and reduce product quality The difficulty of triple bond semi hydrogenation is that the target product is easy to be hydrogenated to form by-product, and the reactant and product are easy to polymerize to form residue in the presence of catalyst Therefore, it is a challenging task to develop a new generation of highly efficient alkynol semi hydrogenation catalyst Recently, the research group of Professor Wang Yong, Department of chemistry, Zhejiang University has made new progress in this field (green chem 2019, 21, 4143-4151) The advanced materials and catalysis research group has always adopted the research mode of combination of basic science and practical application, with the design and development of efficient heterogeneous catalysis materials as the main research direction, and is committed to the pursuit of practical catalysis technology and beautiful basic science The research direction can be divided into: (1) controllable preparation of new catalytic materials Based on the concept of green chemistry, we focus on exploring new and green synthesis methods and developing new catalyst carrier materials, such as shaping biomass and its derivatives into multi-functional carbon materials with controllable morphology and rich channels (2) Development of important industrial catalysts The molecular design, large-scale preparation and application technology of high performance catalysts were studied For example, nitrogen doped carbon (CN) is used as the carrier to prepare high-efficiency heterogeneous catalyst, and the reaction mechanism is studied through experiments and theoretical modeling This strategy provides a general method to prepare high-efficiency supported catalyst, which can effectively cope with a variety of reaction substrates and complex reaction environment Brief introduction to Professor Wang Yong, Professor of Department of chemistry, Zhejiang University, doctoral supervisor, director of Institute of catalysis Top young talents of the "ten thousand talents plan" of the central organization department and winners of the National Excellent Youth Fund In 2002, he graduated from the school of chemical engineering of Xiangtan University, in 2007, he graduated from the Department of chemical engineering of Zhejiang University, in 2007-2009, he was engaged in post doctoral research in the Department of chemistry of Zhejiang University, in 2009-2011, he was engaged in post doctoral research in the Institute of colloid and interface chemistry of Mapu, Germany, and since 2011, he has entered Zhejiang University As the project leader, he has undertaken a number of national and provincial and ministerial projects, such as excellent youth fund of National Natural Science Foundation, general project, outstanding youth fund and key fund of Zhejiang Province, etc Wang Yong's research group is devoted to the research and development of industrial catalysts, especially the research on the supported industrial catalysts based on porous carbon and metal oxides and the related reaction mechanism Many catalysts developed by the research group have been applied in industry, and have produced significant economic and social benefits In 2018, it won the "outstanding contribution award of Youth Science and technology" of China Petroleum and Chemical Industry Federation More than 120 SCI papers were published in J am Chem SOC., NAT Commun., angew Chem Int ed., J catalyst SCI was cited more than 9500 times, h-index 46 More than 20 national invention patents have been authorized Cutting edge scientific research achievements: precise design of high efficiency alkynol semi hydrogenation catalyst at present, the catalyst for the three bond semi hydrogenation in industrial production is mainly Lindlar catalyst However, there are still many problems in Lindlar catalyst: (1) a large number of heavy metal promoters such as lead (PB) and bismuth (BI) need to be added to Lindlar catalyst to improve the selectivity of enols, and the loss of lead and bismuth (especially lead) in the use process will cause serious environmental pollution; (2) Lindlar catalyst is not stable in the aqueous phase, which limits its application range; (3) )Some organic auxiliaries containing N, P and s need to be added to further improve the selectivity of enol, which makes it very difficult to purify later products, reduces product quality, improves production cost, and has certain harm to the environment; (4) even if the above auxiliaries are added, the selectivity of enol in some reactions is still difficult to be higher than 95% when the conversion rate is more than 99% (5) Almost all Lindlar catalysts increase selectivity and cost greatly at the expense of activity Therefore, how to keep the high selectivity of catalyst without sacrificing the activity of catalyst and how to reduce or avoid the use of toxic and harmful promoters is the first difficult problem in the development of high efficiency three bond semi hydrogenation catalyst From the by-product composition of triple bond semi hydrogenation, for example, alkynol, as shown in Figure 1, the side reaction is mainly the further hydrogenation and coupling polymerization of the target product enol In order to inhibit the occurrence of side reactions and improve the yield of target products, the solution of Lindlar catalyst in industry is to poison and isolate the active components by adding heavy metals and organic additives It has been shown that the main active site of three bond semi hydrogenation is the planar Pd atom of Pd nanoparticles, while the main active site of over hydrogenation is the corner position of Pd nanoparticles This means that the three bond semi hydrogenation and over hydrogenation take place at different active sites on the surface of Pd nanoparticles The previous research results of our research group (J catalyst 2017, 350, 13-20) also show that the main reason why the toxic agent Zn improves the selectivity of PD Zn / CN @ ZnO catalyst for alkynol semi hydrogenation is that it covers the edge angle of Pd particles Therefore, it is not necessary to separate the planar Pd atoms in the main reaction path of three bond semi hydrogenation In addition, in the past, the side reactions of double bond coupling mainly focused on olefins or olefin derivatives containing inert substituents, such as ethylene, propylene, etc., so a method of isolating PD active atoms was proposed to inhibit the generation of high polymer by-products such as green oil by double bond coupling This leads to a misunderstanding of the design of three bond semi hydrogenation catalyst, that is, the isolation of active site atoms is necessary Therefore, the existing industrial Lindlar catalyst will use excessive heavy metals and organic additives to fully isolate the surface Pd atoms, resulting in a significant reduction in catalyst activity According to the previous research results of our group, the separation of planar Pd atoms may even lead to the decrease of selectivity This may be one of the reasons why Lindlar catalyst still needs to be combined with organic additives to achieve the target yield in many cases The previous research results of our research group show that the hydroxyl of alkynol will be adsorbed on the catalyst surface during the reaction process, which may realize the separation of three / double bonds on the PD surface and inhibit the generation of high polymerization by-products The self isolation effect of the substituent group of the reactant means that it is not necessary to isolate the active site atom of the catalyst for alkynol semi hydrogenation from the side reaction of polymerization Figure 1 Schematic diagram of alkynol hydrogenation reaction route Figure 2 Schematic diagram of new PD based high efficiency catalyst with edge and corner selective poisoning based on the above considerations, Professor Wang Yong's team proposed a new PD based catalyst design concept of "edge and corner selective poisoning" As shown in Figure 2, because the coordination number of edge atoms on the surface of Pd nanoparticles is lower than that on the plane, and has higher surface energy, according to the thermodynamics theory, the edge positions of Pd nanoparticles will preferentially adsorb and stabilize the toxic agent By controlling the amount of the toxic agent, we can realize the selective poisoning of the edge and corner PD sites and expose the plane PD sites The new PD based catalyst designed based on this concept can theoretically solve the problem that the high activity and selectivity of alkynol semi hydrogenation on the traditional Lindlar catalyst cannot be achieved at the same time In addition, because the integrity of the active site of planar PD is preserved, the new catalyst may even have higher selectivity In the process of partial alkynol semi hydrogenation, no organic assistant is needed to further improve the yield, thus simplifying the purification steps and improving the product quality In recent years, Professor Wang Yong's research group has carried out a series of cooperation with Zhejiang XinHeCheng Co., Ltd., a major vitamin E and vitamin a manufacturer in the world, on the development of alkynol hydrogenation catalyst, and has made a series of achievements in theoretical innovation and industrial practice Early research group (J catalyst., 2017, 350, 13-20) developed a PdZn / CN @ ZnO catalyst based on the theory that the edge position of Pd particles is responsible for the hydrogenation of alkynol, which shows excellent performance in selective hydrogenation of alkynol without adding toxic and harmful lead and bismuth Although Zn poisoned the edge and corner position of PD, it was not selective Zn also occupied the plane position, resulting in the decrease of catalyst activity Moreover, in practical application, organic auxiliaries such as N, P, s should be added to further improve the selectivity of enol In order to solve this problem, our group chose in to replace Zn to develop PD in / In2O3 catalyst By controlling the reduction temperature, we realized the control of different toxic degree on the surface of Pd nanoparticles As shown in Figure 3, with the increase of reduction temperature, the coating layer on the surface of Pd nanoparticles is more dense The above results are further confirmed by co-ir and co-tpd (Fig 4) Before 200 ℃, in selectively poisoned the edges and corners of Pd nanoparticles, and when the reduction temperature was over 200 ℃, PD plane began to be poisoned Accordingly, with the increase of reduction temperature, the selectivity of mby semi hydrogenation also increased first and then decreased (Fig 5) The highest selectivity is 95% at 99% conversion rate without adding organic assistant, and the corresponding TOF value is 2 times higher than PdZn / CN @ ZnO developed by the research group in the early stage However, under this reaction condition, the traditional industrial Lindlar catalyst has no activity This shows that the poisoning of planar PD site is not conducive to both the improvement of selectivity and the maintenance of activity, so the structural design of high-efficiency alkynol semi hydrogenation catalyst should be as shown in Figure 2, only poisoning the edge and corner sites, while retaining the planar sites Fig 3 Coating degree of Pd nanoparticles at different reduction temperature Fig 4 (a) co-ir and (b) co-tpd of PD in / in 2O 3 catalysts treated at different reduction temperature Fig 5 Reaction performance test of catalysts treated at different reduction temperature Considering the industrial reaction conditions, the research team continued to investigate the mby semi hydrogenation performance comparison of industrial Lindlar catalyst and self-made PD in / In2O3 new catalyst under the reaction conditions of solvent-free and organic additives free The results are shown in Figure 6 The TOF of PD in / in 2O 3 catalyst is 4.5 times higher than that of industrial Lindlar catalyst, and the selectivity is up to 98% In the industrial application, it can meet the requirement of no need to add organic additives, while the industrial Lindlar catalyst can only reach 93% This is the first case in which alkynol semi hydrogenation does not need additional organic additives In addition, the catalyst has good universality for the substrate and good circulation stability It is the first time that the high activity and
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