Water-Promoted Palladium Catalysts for Methane Oxidation
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Water-Promoted Palladium Catalysts for Methane Oxidation Jiongliang Yuan • Yan Wang • Cunjiang Hao
Received: 10 January 2013 / Accepted: 25 March 2013 / Published online: 3 April 2013 Ó Springer Science+Business Media New York 2013
Abstract A water-tolerant, active and high-selective palladium catalyst, (2,20 -bipyridine) dichloropalladium(II) is proposed for the oxidation of methane to a methanol derivative with molecular oxygen as the oxidant at temperatures below 120 °C, and its activity can be increased by three times at 100 °C when the volume ratio of water to CF3COOH solvent is 1:5. In addition, the addition of perfluorooctane can enhance the yield of methanol further. Keywords Homogeneous catalysis C–H bond activation Partial oxidation Methane Molecular oxygen
1 Introduction Indirect reaction routes for obtaining methanol from methane via syngas have already been adopted in chemical industry; however, the production of syngas is an energyintensive and cost-intensive process. Low-temperature oxidation of methane to methanol has become attractive since 1970s, due to its energy and cost effectiveness. 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
J. Yuan (&) Y. Wang Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100019, 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
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selectivity of methanol are very low [1]. In a non-aqueous solution, many effective catalysts, such as heteropoly acids and transition metal salts, have already been developed [2–9]. In (CF3CO)2O and/or CF3COOH solvents, with the catalysis of vanadium-containing heteropolyacids, methane can be oxidized to CF3COOCH3 and other oxygenates [5–7]. (CF3CO)2O is used to remove the water generated in methane oxidation, therefore to improve the yield of CF3COOCH3 [5–9]. As the radical group mechanism is involved, the selectivity is relatively low. In a concentrated H2SO4 solution, a stable platinum complex, (bpym)PtCl2, developed by Catalytica, could directly oxidize methane to a methanol derivative with a higher yield and selectivity [3]. However, its reactivity was found to be extremely sensitive to the appearance of water, i.e., the catalyst activity decreases rapidly with the water generated during the reaction [10–12]. The adverse effect of water at only trace amount can be inhibited by introducing ionic liquid in catalytic system, whereas the role of ionic liquid becomes less important as the concentration of water increases [12]. So far, reports on water-tolerant, active and high-selective catalysts for oxidation of methane at a low temperature have not been found yet. In our previous work, a catalytic system, palladium acetate (Pd(OAc)
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