Journal of Alloys and Compounds 465 (2008) 361–366 Isoprene gas phase hydrogenation catalyzed by ThNi 2 and UNi 2 Joaquim Badalo Branco ∗ , Ant ´ onio Pereira Gonc ¸alves, Ant´ onio Pires de Mato Departamento de Qu´ ımica, Instituto Tecnol´ ogico e Nuclear, Estrada Nacional 10, P-2686-953 Sacav´ em Codex, Portugal Received 4 May 2007; received in revised form 16 October 2007; accepted 20 October 2007 Available online 26 October 2007 Abstract The study of isoprene (2-methyl-1,3-butadiene) gas phase hydrogenation on ThNi 2 and UNi 2 was undertaken and the effect of the 5f element on nickel catalytic behavior investigated. At nearly steady state, the reaction products were isopentane and isopentenes (2-methyl-2-butene, 2-methyl- 1-butene and 3-methyl-1-butene). The total selectivity to isopentenes was higher on ThNi 2 (∼80 mol%) than on UNi 2 (∼50 mol%) but, in both cases lower than that on pure Ni (∼96 mol%). The sum of 2-methyl-2-butene + 2-methyl-1-butene selectivities (valuable products for the tert-amyl methyl ether process) was ∼75 mol% on ThNi 2 , whereas on UNi 2 it was significantly lower (∼50 mol%). ThNi 2 and UNi 2 total selectivity to isopentenes is nearly time invariant. The difference of catalytic properties between ThNi 2 and UNi 2 can be explained by electronic transfer from the 5f element to Ni that generates an electronic density supply on nickel, which is higher on ThNi 2 . © 2007 Elsevier B.V. All rights reserved. Keywords: Intermetallic compounds; Nickel; Actinides; Isoprene; Selective hydrogenation 1. Introduction The hydrogenation of highly unsaturated hydrocarbons forms the basis of large scale processes of considerable importance, namely those arising from conversion processes like naphtha steam-cracking or fluid catalytic cracking and concerning the hydrogenation of diene hydrocarbons to olefin [1,2]. Palladium is the most active and selective metal for these hydrogenation reactions [3–10]. Isopentenes are the desired species in the C5 gasoline fraction, used as the feedstock for the tert-amyl methyl ether process (TAME) [7,11], where it is important to increase the conversion of alkynes and alkadienes to isopentenes, while reducing the further reaction to isopentane. The hydrogenation of 1,3-butadiene and isoprene (2-methyl- 1,3-butadiene) are often chosen as model reactions. Isoprene hydrogenation is a consecutive reaction that by 1,2 addition produces 3-methyl-1-butene (3M1B) and 2-methyl-1-butene (2M1B), whereas 2-methyl-2-butene (2M2B) is formed either by 1,4 addition or, at higher conversion (>20%), via double bond isomerisation on 2M1B or 3M1B [7,12]. Further hydro- ∗ Corresponding author. Tel.: +351 219946116; fax: +351 219941455. E-mail address: jbranco@itn.pt (J.B. Branco). genation of these isopentenes gives isopentane, the undesired product. On heterogeneous Pd catalysts, the three methylbutene iso- mers (2M1B, 3M1B and 2M2B) are approximately produced in the ratio of 1:1:2, and very little isopentane. A simple mecha- nistic scheme has been suggested to explain this ratio [4] and aspects like deactivation [13] and catalyst rejuvenation [10], metal dispersion and particle size [3,7] or catalyst preparation procedure [3] on the activity and selectivity have been reported in the literature. The tests with supported palladium catalysts showed that catalyst deactivation is mainly due to coke formation via poly- merization of polynuclear aromatics and/or polyolefins [13] and that isoprene conversion increases with increasing Pd dispersion, i.e., lower particle size, while the selectivity to total isopentenes decreases [7]. This effect was attributed to: (i) increase of the number of active sites of the catalysts to be further used for the hydrogenation of isopentenes to isopentane and (ii) to a higher adsorption strength between isopentenes and the catalyst active site, e.g. on small Pd particles with electron-deficient character [7,10], which leads to a decrease of the selectivity to isopentenes because the desorption is slower than the hydrogenation rate to isopentane. On the other hand, Bachir et al. [3] have studied the effect of adding iron and found that the catalyst preparation 0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.10.086