Journal of Molecular Catalysis A: Chemical 215 (2004) 95–101 Active phases of supported cobalt catalysts for 2,3-dihydrofuran synthesis Ludmila Leite a,∗ , Vladislavs Stonkus a , Kristine Edolfa a , Luba Ilieva b , Donka Andreeva b , Ludmila Plyasova c , Janusz W. Sobczak d , Sorana Ionescu e , Gabriel Munteanu e a Latvian Institute of Organic Synthesis, 21 Aizkraukles Str., Riga LV-1006, Latvia b Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofija, Bulgaria c Boreskov Institute of Catalysis, Russian Academy of Sciences Siberian Division, 5 Acad. Lavrentjev Str., Novosibirsk, 630090, Russia d Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52 Str., 01-224 Warszawa, Poland e Romanian Academy Institute of Physical Chemistry “I.G. Murgulescu”, 202 Splaiul Independentei St., 77208-Bucharest, Romania Received 24 October 2003; accepted 11 November 2003 Abstract Dehydrogenation of 1,4-butanediol to 2,3-dihydrofuran over kaolin-supported Co and Co–Au catalysts has been investigated. Catalytic test and XRD analysis show that the presence of metallic cobalt with hexagonal structure is favourable for selectivity to 2,3-dihydrofuran of the reaction studied. It was established by XPS method that an optimal for the reaction selectivity Co 0 /Co 2+ ratio in Co/kaolin and Co–Au/kaolin catalysts exists. Quantum chemical calculations suggest that the initial step of 1,4-butanediol dehydrogenation on cobalt catalyst surface may be the cleavage of O–H bond to form alkoxide species on Co 2+ ion. Based on the effect of metallic and ionic cobalt on the catalyst selectivity, it could be presumed that both cobalt species are involved in the rate-determining step in dehydrogenation of 1,4-butanediol into 4-hydroxybutanal intermediate. © 2004 Elsevier B.V. All rights reserved. Keywords: Cobalt catalyst; Gold promotion; 1,4-Butanediol; 2,3-Dihydrofuran; Dehydrogenation 1. Introduction Dehydrogenation of alcohols gives commodity chemicals of a considerable industrial use, on which many studies are focused. Dehydrogenation of methanol, ethanol, propanol, 2-propanol, octanol, and cyclohexanol proceeds mainly in the presence of metal oxides having basic properties [1–4] and metallic or bimetallic catalysts [5,6]. The role of cobalt either in metallic or in ionic state is not yet clear, and the nature of the active sites in dehydro- genation reactions is still debated. Now more and more data indicate that ionic species may play an important role in de- hydrogenation. On the other hand, it was established that in the case of cyclohexanol dehydrogenation on metallic cobalt catalyst, the incomplete reduction of the metal oxide favours the cyclohexene formation (side reaction) by direct cyclo- hexanol dehydration [6]. ∗ Corresponding author. Tel.: +371-7551822; fax: +371-7821038. E-mail address: leite@osi.lv (L. Leite). The conversion of 1,4-butanediol on supported cobalt, copper and platinum catalysts has been studied [7–11]. The reaction occurs through several sequence reactions (such as shown in Scheme 1) leading to the formation of 2,3-dihydrofuran and tetrahydrofuran. This scheme includes 1,4-butanediol dehydrogena- tion into 4-hydroxybutanal. Our experimental data sug- gests that dehydrogenation is a rate-limited stage in the synthesis of 2,3-dihydrofuran [8]. Almost quantitative 2,3-dihydrofuran formation is a result of the subsequent fast isomerization of 4-hydroxybutanal and dehydration of 2-hydroxytetrahydrofuran over the support. Recently, we established that the modification of sup- ported cobalt catalyst by gold is favourable for 2,3-dehydro- furan synthesis, concerning not only the enhanced catalyst reducibility, which is desirable in order to lower the pre- treatment temperature, but also the catalyst selectivity [7,12]. The aim of the present study is to throw light on the active phases regarding a possible participation of cobalt in metallic and ionic states in 1,4-butanediol transforma- tion to 2,3-dihydrofuran, over cobalt/kaolin catalysts, being non-promoted and promoted by gold. 1381-1169/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.molcata.2003.11.036