Partial Oxidation of Methane with the Catalysis of Palladium(II) and Molybdovanadophosphoric Acid Using Molecular Oxygen
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Partial Oxidation of Methane with the Catalysis of Palladium(II) and Molybdovanadophosphoric Acid Using Molecular Oxygen as the Oxidant Jiongliang Yuan • Lu Liu • Lanlan Wang Cunjiang Hao
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Received: 3 September 2012 / Accepted: 16 October 2012 Ó Springer Science+Business Media New York 2012
Abstract With the catalysis of K2PdCl4 and H5PMo10V2 O40 in CF3COOH, methane can be oxidized into CH3COOH and CF3COOCH3 using molecular oxygen as the oxidant at a low temperature. H5PMo10V2O40 is a reversible oxidant that allows to retain Pd(II) in CF3COOH and thus to complete a two-step catalytic cycle of oxidation of methane by molecular oxygen; in addition, it can catalytically oxidize methane into CH3COOH and CF3COOCH3. Keywords Homogeneous catalysis C–H bond activation Partial oxidation Methane Molecular oxygen
1 Introduction The activation of methane has attracted much attention due to its high abundance in natural gas and its low activity. Current technologies for the activation of methane proceed by generation of carbon monoxide and hydrogen (syngas), followed by converting syngas into liquid products through Fischer–Tropsch chemistry. However, the production of syngas is an energy-intensive and cost-intensive process. In contrast, direct, low-temperature, partial oxidation of methane becomes promising.
J. Yuan (&) L. Liu L. Wang Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China e-mail: [email protected] C. Hao Department of Experimental Teaching, Tianjin University of Traditional Chinese Medicine, and Tianjin Key Laboratory of Chemistry and Analysis of Chinese Materia Medica, Tianjin 300193, People’s Republic of China
Although methane can be oxidized into methanol and chloromethane with PtCl62- as the oxidant and with PtCl42- as the catalyst in an aqueous solution, the yield and selectivity of methanol are very low [1]. Periana et al. [2, 3] have reported that high conversion of methanol derivatives from methane could be obtained with the catalysis of Hg(II) or Pt(II) in concentrated sulfuric acid. The metal ion M(II) (M=Hg, Pt) reacts with methane by an electrophilic displacement mechanism to produce CH3MOSO3H which can readily decompose to CH3OSO3H and the reduced metal species. The catalytic cycle is completed by the reoxidation of the reduced metal species with concentrated sulfuric acid to regenerate M(II) [2, 3]. Pt(II) is more efficient than Hg(II) during the catalysis reaction, however, it will be irreversibly reduced in bulk metal, which results in fast deactivation of catalysts and steep decrease of selectivity [2]. In order to inhibit the irreversible reduction, Periana et al. [3] further developed a stable platinum ligand (bpym)PtCl2, which could directly oxidize methane into a methanol derivative with higher yield and selectivity. About 90 % methane conversion and 81 % selectivity could be obtained at 220 °C for 2.5 h [3]. Although Hg(II) and Pt(II) salts can give high catalytic activity, Hg(II)
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