Catalysis Today 198 (2012) 338–344 Contents lists available at SciVerse ScienceDirect Catalysis Today j ourna l ho me p ag e: www.elsevier.com/lo cate/cattod Catalytic study of the conversion of ethanol into 1,3-butadiene E.V. Makshina, W. Janssens, B.F. Sels ∗ , P.A. Jacobs Centre for Surface Chemistry and Catalysis, Faculty of Bioscience Engineering, KU Leuven, Kasteelpark Arenberg, 23, Box 2461, 3001 Heverlee, Belgium a r t i c l e i n f o Article history: Received 27 February 2012 Received in revised form 2 May 2012 Accepted 5 May 2012 Available online 21 June 2012 Keywords: Ethanol 1,3-Butadiene Biomass conversion Magnesia–silica catalyst Silver catalysts Multifunctional catalysis a b s t r a c t Direct synthesis of 1,3-butadiene (BD) from ethanol has been studied using magnesia–silica catalysts doped with transition metal(oxide)s. The effects of Mg/Si ratio, the synthesis procedure, and the dopant concentration were studied. It was demonstrated that modification of the magnesia–silica binary system using a consecutive impregnation step significantly increases the ethanol conversion rate and BD yield. The BD yield higher than 55 mol.% was obtained at full ethanol conversion for materials containing Cu and Ag modifiers. The influence of the reaction temperature and the ethanol concentration in the feed was also investigated. This investigation led to high BD productivity (>0.15 g BD g cat -1 h -1 ) and high BD concentration in the product stream (>10,000 Vppm). © 2012 Elsevier B.V. All rights reserved. 1. Introduction Today 1,3-butadiene (BD) is an important building block for the chemical industry. The polymerization of BD with itself and with other olefin monomers represents its largest commercial use. The commercially most important polymers are styrene–butadiene rubbers, polybutadiene, styrene–butadiene latex, acrylonitrile–butadiene–styrene polymer and nitrile rubber. Since the early seventies, the dominant technology for producing BD is the cracking of naphtha, where BD is obtained as a co- product. As the growth of ethylene production outpaced the growth of BD demand, the oversupply of BD led to shut down of the all on-purpose BD production technologies. The recent trends in light- ening of the feedstock of steam crackers reduce BD supply and may potentially lead to a shortage in BD production in coming years. Currently a lot of attention is paid to the usage of alternative and renewable resources for fuels and chemicals. Due to politi- cal incitements as well as emerging tax policies, there is a huge incentive to use monomers from biological origin. Ethanol is one of the most relevant potential sources of “bio”-carbon today [1]. Pro- duction of bioethanol occurs via fermentation and is industrially applied with sugar and corn feedstocks, while the second genera- tion bioethanol from lignocellulosic feedstock is under extensive development [2]. Catalytic conversion of ethanol into BD is an old industrially proven route. From the 1920s to the early 1960s, ∗ Corresponding author. Tel.: +32 16321593; fax: +32 16321998. E-mail addresses: ekaterina.makshina@biw.kuleuven.be (E.V. Makshina), bert.sels@biw.kuleuven.be (B.F. Sels), pierre.jacobs@biw.kuleuven.be (P.A. Jacobs). ethanol was converted to BD, hydrogen, and water at 400–450 ◦ C according to a one-step process developed by Sergey Lebedev using a variety of (mixed) oxide catalysts [3–5]. High yields with selec- tivity to BD up to 72 mol.% have been reported [6]. Unfortunately, these reports did not disclose details concerning the composition of the catalyst. Simultaneously, Carbide and Carbon Chemicals Corpo- ration performed the industrial manufacturing of BD from ethanol in the USA using a two-step process over 2% of tantalum oxide on silica [7]. This technology, which is also known as Ostromyslen- sky’s process, included the partial ethanol dehydrogenation to acetaldehyde, followed by transformation of the mixture of ethanol and acetaldehyde into BD with 30–35% yield with selectivity 60%. The mechanism of the ethanol to BD transformation is extremely complicated and is still subject of debate. However, one gener- ally accepts the involvement of the following five principal steps (Fig. 1) [6,8–12]: (1) acetaldehyde formation from ethanol; (2) aldol condensation of acetaldehyde to acetaldol; (3) dehydration of acetaldol to crotonaldehyde; (4) Meerwein–Ponndorf–Verley reac- tion between crotonaldehyde and ethanol to obtain crotyl alcohol and acetaldehyde; and (5) dehydration of crotyl alcohol to BD. A possible reaction scheme of the main molecular transformations is summarized in Fig. 1 [9]. Obviously, such complex reaction net- work of different reaction types (e.g., dehydration, MPV reduction and aldol condensation) entails a multifunctional heterogeneous catalyst with a subtle balance of the amount and strength, and the ideal proximity of acid/base and redox sites, in order to provide the ideal kinetics. Various materials have been proposed as catalysts to per- form this reaction [9–11,13–31]. Among all catalysts that were 0920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cattod.2012.05.031