Journal of Molecular Catalysis A: Chemical 380 (2013) 57–60 Contents lists available at ScienceDirect Journal of Molecular Catalysis A: Chemical j ourna l ho me page: www.elsevier.com/locate /molcata Hydrogenation of lactic acid to propylene glycol over a carbon-supported ruthenium catalyst Hyuk Jang a , Sung-Hwan Kim a , Duwon Lee a , Sang Eun Shim a,b , Sung-Hyeon Baeck a,∗ , Beom Sik Kim b , Tae Sun Chang b a Department of Chemistry and Chemical Engineering, Inha University, Incheon, South Korea b Korea Research Institute of Chemical Technology, 141 Gajeongro, Yuseong, Daejeon 305-600, South Korea a r t i c l e i n f o Article history: Received 2 September 2013 Accepted 8 September 2013 Available online 17 September 2013 Keywords: Lactic acid Propylene glycol Hydrogenation Ruthenium Carbon support a b s t r a c t Catalytic hydrogenation of lactic acid to propylene glycol is performed in a high-pressure batch reactor over ruthenium on various carbon supports (i.e., VulcanXC-72, ketjen black, CNTs, CNFs, and graphite) prepared using the incipient wetness impregnation method. The crystallinity of the synthesized catalyst is investigated via X-ray diffraction, and the particle sizes are determined using transmission electron microscopy. The surface areas of the synthesized catalysts are analyzed using the BET method; the cat- alytic activity correlates remarkably with the BET surface area. The yield of propylene glycol increases with pressure, and the highest yield is achieved at 130 ◦ C. The catalytic activity is strongly dependent on the type of support. Among the catalysts tested, Ru on ketjen black shows the highest yield of propylene glycol. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Lactic acid is a very useful raw material for the food and medical industries, and its consumption has increased steadily. The produc- tion of lactic acid by fermentation of biomass is important to meet the increasing demand. Via fermentation, lactic acid can be gener- ated from renewable sources such as refined carbohydrates derived from agricultural crops [1,2] and waste biomass [3]. Lactic acid is known to be very reactive because it contains both hydroxyl and carboxy functional groups. Accordingly, it can be converted into a variety of chemicals through polymerization [3], condensation [4–6], dehydration [7], esterification [8,9], and oxidation [10]. Propylene glycol is widely used in foods, consumer products, and chemical applications and is produced industrially via the hydration of propylene oxide [11]. Propylene glycol production from lactic acid via a very good method was reported in the 1930s (Fig. 1). However, in general the catalytic conversion of lactic acid to propylene glycol requires high temperature and pressure. Dumesic et al. reported the conversion of lactic acid to propylene glycol over a silica-supported copper catalyst [12]. They proposed that hydroxyl acryl species were formed by dissociative adsorption of lactic acid; successive hydrogenation of the adsorbed species was thought to comprise the main mechanism for the production of propylene glycol. ∗ Corresponding author. Tel.: +82 32 860 7474; fax: +82 32 860 8908. E-mail address: shbaeck@inha.ac.kr (S.-H. Baeck). Miller et al. [13] investigated the production of propylene glycol from lactic acid over various catalysts and reported a high yield of propylene glycol using ruthenium supported on activated carbon prepared via impregnation. According to their results, carbon is a promising support because of its inertness and stability in aqueous solution. In the present work, ruthenium was supported on five differ- ent types of carbon (i.e., VulcanXC-72, ketjen black (KNB), carbon nanotubes (CNTs), carbon nanofibers (CNFs), and graphite) via the incipient wetness impregnation method. The resultant supported ruthenium catalysts were characterized by X-ray diffraction (XRD), the Brunauer–Emmett–Teller (BET) method, and high-resolution transmission electron microscopy (HR-TEM). The catalytic activities of the catalyst towards the conversion of lactic acid into propylene glycol were investigated in a liquid- phase batch reactor, and the influence of the reaction temperature and pressure on lactic acid conversion was also studied. The main goal of this study is to investigate the effect of the support on the catalytic activity of ruthenium. 2. Experimental 2.1. Preparation and characterization of supported ruthenium catalyst All carbon supports used in this study were obtained from commercial sources: VulcanXC-72 from Carbot International, ket- jen black from Mitsubishi Chemical, CNTs from Iljin Nanotech, 1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molcata.2013.09.006