Oxidation of Glycerol with Oxygen in a Base-free Aqueous Solution over Pt/AC and Pt/MWNTs Catalysts
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Oxidation of Glycerol with Oxygen in a Base-free Aqueous Solution over Pt/AC and Pt/MWNTs Catalysts Jing Gao Æ Dan Liang Æ Ping Chen Æ Zhaoyin Hou Æ Xiaoming Zheng
Received: 5 November 2008 / Accepted: 1 January 2009 / Published online: 17 January 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Catalytic oxidation of glycerol with molecular oxygen to glyceric acid was performed in a base-free aqueous solution over Pt/MWNTs and Pt/AC catalysts. Pt/MWNTs was more active for the easier accessibility of Pt on the external wall of MWNTs, and the initial TOF reached 10.63 mmol min-1/mmol-Pt. The easier accessibility of glycerol to Pt particles on MWNTs was confirmed by Raman. Keywords MWNTs
Glycerol oxidation Glyceric acid Pt
1 Introduction The use of biorenewable feedstock is of crucial importance for a sustainable society because of the rapidly rising price of crude oil. Biodiesel is a renewable biofuel which is popularly recommended for its recycle usage of CO2 and lower emission of particles, CO and HC in exhaust. During biodiesel production via transesterification of oils from plants such as rape, soya and palm, 100 kg of glycerol (also known as glycerin) is produced for every ton of biodiesel. A major surplus of glycerol has resulted from the increasing expansion of biodiesel production, and currently disposal of surplus glycerol is by incineration. Catalytic conversion of glycerol to value-added products has attracted much attention in the past few years [1–3]. Among the published works, an increasing number of studies were focused on chemoselective oxidation of
J. Gao D. Liang P. Chen Z. Hou (&) X. Zheng Key Lab of Applied Chemistry of Zhejiang Province, Department of Chemistry, Zhejiang University, Xixi Campus, Hangzhou 310028, People’s Republic China e-mail: [email protected]
glycerol to valuable oxygenated derivatives such as glyceric acid (GLYA), dihydroxyacetone (DIHA), hydroxypyruvic acid (HPYA) and tartronic acid (TARAC) [4–16]. And now, these oxygenated derivatives are either synthesized via costly and polluting stoichiometric oxidants (e.g. potassium permanganate, nitric acid or chromic acid) or produced via fermentation processes of low productivity [6, 17]. But the reported catalytic synthesis routes depend strongly on the reaction conditions (pH, temperature, substrate to metal ratio) and the nature of catalyst (metal, particle size and support). Kimura et al. [4] firstly reported the catalytic oxidation of glycerol in 1993. They found that GLYA was the main product on Pt/C during glycerol oxidation, but the conversion of glycerol was quite low without the addition of alkali. Besson et al. [5] investigated the oxidation of glycerol in a wide ranged pH value (2–11) on a series of catalysts, and they found that the selectivity to GLYA can reach 70% on Pd/C (at pH 11), while the selectivity of GLYA decreased to 55% on Pt/C (at pH 7). Hutchings and co-workers [6–8] performed the oxidation of glycerol over a series of Au-based catalysts. They disclosed that Au particles sized in
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