Cyclohexene Epoxidation Catalysts Based on Porous Aromatic Frameworks
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ohexene Epoxidation Catalysts Based on Porous Aromatic Frameworks L. A. Kulikova, *, V. A. Yarchaka, A. V. Zolotukhinaa, b, A. L. Maksimova, b, and E. A. Karakhanova aFaculty
bTopchiev
of Chemistry, Moscow State University, Moscow, 119991 Russia Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected] Received April 28, 2020; revised May 12, 2020; accepted May 12, 2020
Abstract—Molybdenum and tungsten catalysts, PAF-30-Mo and PAF-30-W, synthesized based on a porous aromatic framework PAF-30 have been tested in the epoxidation of cyclohexene with tert-butyl hydroperoxide. The influence of the temperature and the substrate to oxidant ratio on the characteristic features of the process has been studied. It has been shown that the catalysts exhibit high activity and make it possible to obtain cyclohexene epoxide in a high yield; however, they lose their activity over time due to the leaching of the metal from the pores of the polymer. Keywords: nanoparticles, heterogenous catalysis, epoxidation, molybdenum DOI: 10.1134/S0965544120090169
Epoxides constitute a very important class of organic compounds in modern polymer and petrochemical industries. They are widely used in fine organic synthesis, in the production of dyes, surfactants, drugs, plasticizers, polymers, etc. [1–3]. A general method for the preparation of epoxides is selective oxidation of olefins. However, the oxidation method depends on the olefin structure. Thus, the industrial process for the production of ethylene oxide is based on the direct oxidation of ethylene with atmospheric oxygen over silver catalysts [4]. The oxidation of propylene under the same conditions is not selective and leads to the formation of acrolein as the second product. Due to this, the production of propylene oxide is carried out using either the chlorohydrin process [4] or more modern processes of propylene oxidation with organic hydroperoxides in the presence of various catalysts [1]. Despite the success of industrial implementation of the new processes for the production of epoxides, the development of new catalysts for the epoxidation of olefins is still a demanding task. Generally, olefin epoxidation catalysts are based on complexes or salts of various transition metals, such as molybdenum [5, 6], titanium [7], vanadium [8], and tungsten [9]. These metals in the highest oxidation state possess low oxidation potentials, due to which they quite readily form peroxide compounds and exhibit high activity in the epoxidation reaction [10]. Of the metals in question, molybdenum and its various coordination compounds, e.g., Mo(CO)6, MoO2(acac)2, MoO2-phthalocyanine, MoO2(octaneMoO2(cyclohexane-1,2-diol)2, and 1,2-diol)2,
MoO2(oxinate)2, manifest the highest activity [11]. Due to their activity, as well as availability and relatively low cost, catalysts based on molybdenum became widespread both in laboratory and in industry [12]. For example, molybdenum naphthenate is used as a catalyst for the production of propylene o
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