Effective and Reusable Pt Catalysts Supported on Periodic Mesoporous Resols for Chiral Hydrogenation
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Effective and Reusable Pt Catalysts Supported on Periodic Mesoporous Resols for Chiral Hydrogenation Xiaohong Li Æ Yali Shen Æ Rong Xing Æ Yueming Liu Æ Haihong Wu Æ Mingyuan He Æ Peng Wu
Received: 7 November 2007 / Accepted: 30 November 2007 / Published online: 18 December 2007 Ó Springer Science+Business Media, LLC 2007
Abstract Platinum nanoparticles supported on periodic mesoporous resols by simple impregnation serve as effective, robust and remarkably reusable catalysts after chirally modified with cinchonidine for the asymmetric hydrogenation of ethyl pyruvate, affording up to 62% enantiomeric excess (ee) and a constant activity after 25th re-use. They can also catalyze the reaction in an environmentally benign manner by using water as a solvent. Keywords Periodic mesoporous resols Pt/FDU-15 Enantioselective hydrogenation Ethyl pyruvate 1 Introduction Enantioselective hydrogenation of a-functionalized ketones catalyzed by supported platinum catalysts modified with cinchona alkaloids and related modifiers has been considered as one of the milestones of heterogeneous asymmetric catalysis, and extensive studies have been carried out on this system in the past decades [1–6]. Most of these studies focused on commercially available 5.0 wt.% Pt/Al2O3 catalysts [7–16], e.g. E 4759 from Engelhard or JMC 5 R 94 from Johnson Matthey, or 6.3 wt.% Pt/SiO2 catalysts [17, 18], e.g. EUROPT-1. New types of catalysts such as platinum colloids [19] and Pt particles supported on X. Li (&) Y. Shen R. Xing Y. Liu H. Wu M. He P. Wu (&) Department of Chemistry, Shanghai Key Laboratory of Green Chemistry and Chemical Processes, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062, China e-mail: [email protected] P. Wu e-mail: [email protected]
inorganic materials other than Al2O3 and SiO2 have also been explored at around the same time. Moderate to good enantiomeric excesses (ees) were obtained with Pt/MCM41 [20–22], Pt/HNaY [23], Pt/clay [24, 25], Pt/LDH [26], and Pt/SWNTs catalysts [27]. Due to use of the expensive noble metal catalysts and to enhance productivity, the continuous operation in a fixedbed reactor for the asymmetric hydrogenation of a-functionalized ketones has received much attention in recent years [1, 28–32]. Continuous feeding of minute amounts of chiral modifier can maintain the ee of product [29, 31]. Even though time-required charging, discharging and catalyst handling are needed, the recycling of Pt/Al2O3 catalyst was realized using a batch reactor [33–35]. In ethanol, the catalyst can be reused for at least thrice without distinct decrease in ee values and conversions, but decrease in activity [33]. In toluene medium, ‘‘an increase in ee on reuse’’ of 10–20% was observed under the mild experimental conditions depending on the reaction conditions [34]. However, when the reaction was performed in acetic acid, the relatively inferior reusability of Pt/Al2O3 catalyst was observed [34, 35]. Organic polymers have also attracted much more attention in recent years due to
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