Homogeneous Metal-Complex Catalyst Systems in the Partial Oxidation of Propane with Oxygen
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geneous Metal-Complex Catalyst Systems in the Partial Oxidation of Propane with Oxygen E. G. Chepaikina, *, G. N. Menchikovaa, and S. I. Pomogailoa aMerzhanov
Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia *e-mail: [email protected] Received November 15, 2019; revised June 15, 2020; accepted July 10, 2020
Abstract—The effect of copper compounds and phosphorus–molybdenum–vanadium heteropoly acids (HPAs) H5PMo10V2O40 and H7PMo8V4O40 used as cocatalysts in the cooxidation of propane and CO in the presence of rhodium, palladium, and platinum compounds in an aqueous AcOH medium has been studied. It has been shown that these HPAs are fairly effective; however, in catalyst systems with rhodium and palladium compounds, these HPAs are inferior to Cu(I,II). The inner-sphere and outer-sphere reaction mechanisms have been studied as the most probable oxidation mechanisms; the contribution of each of the mechanisms to the overall process has been determined. Keywords: alkanes, partial oxidation, carbon monoxide, rhodium, palladium, and platinum complexes, reaction mechanism, heteropoly acids DOI: 10.1134/S096554412011002X
Alkanes of natural and associated petroleum gases are an available inexpensive feedstock for the production of key oxygen-containing compounds of organic and petrochemical synthesis, namely, alcohols, aldehydes, ketones, and carboxylic acids. To date, the use of this feedstock has been limited to conversion to synthesis gas and the subsequent synthesis of methanol or hydrocarbons by the Fischer–Tropsch reaction [1, 2]. Under normal conditions, alkanes are relatively inert compounds. Conventional heterogeneous catalysts exhibiting activity at relatively high temperatures are nonselective in the direct oxidation of alkanes because of the occurrence of deep oxidation reactions [3]. Homogeneous catalysts and catalyst systems are active at lower temperatures and characterized by high selectivity [4]. The discovery of the homogeneous activation of methane by Shilov et al. [5] in 1969 has given an impetus to a rapid development of this field of chemistry. Over the past 50 years, an extensive amount of experimental and theoretical data has accumulated [6–12]; however, a catalyst appropriate for commercialization has not yet been developed. Various compounds, such as H2O2, K2S2O8, C6H5IO, organic peroxides, and hydroperoxides, were studied as oxidizers. It was found that the use of H2O2 for methane oxidation to methanol is unprofitable [13]. Most probably, the commercialization of oxidation processes will require the use of molecular oxygen as a feed oxidizer, particularly, in the case of C1–C4
alkanes. In this context, oxygen activation is added to the fairly complicated stage of C–H bond activation. To date, two main approaches to alkane activation can be distinguished. According to the first approach, alkane activation occurs in the inner coordination sphere of a catalytically active metal complex to form a metal–alkyl bond (inner
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