Thermochimica Acta 419 (2004) 283–290 The kinetics of H 2 adsorption on supported ruthenium catalysts Hsin-Yu Lin, Yu-Wen Chen ∗ Department of Chemical and Materials Engineering, Nanocatalysis Research Center, National Central University, Chung-Li 32054, Taiwan Received 2 October 2003; received in revised form 5 March 2004; accepted 9 March 2004 Available online 7 May 2004 Abstract Ruthenium catalysts supported on SiO 2 , Al 2 O 3 and TiO 2 were prepared by the impregnation method. Temperature-programmed desorption (TPD) method was applied to investigate the kinetics of hydrogen adsorption/desorption on these catalysts. All the TPD results show two-peak profile, except Ru/SiO 2 . The low-temperature peak was assigned to the hydrogen adsorbed on the Ru metal. The high-temperature peak was attributed to the spillover of hydrogen atoms from metal to the support. Both are activated process. The amount of adsorbed hydrogen increased with increasing adsorption temperature, and the maximum adsorption occurs at above 200 ◦ C. The activation energy of adsorption is a function of catalyst support and the reduction temperature. It decreases in the order of Ru/TiO 2 (500 ◦ C reduction)> Ru/Al 2 O 3 > Ru/TiO 2 (300 ◦ C reduction)> Ru/SiO 2 . The results demonstrated that the strong metal–support interaction exerted on Ru/TiO 2 would suppress hydrogen chemisorption at room temperature due to its high activation energy. However, hydrogen chemisorption on Ru/TiO 2 was not suppressed at high temperature. One is able to measure the Ru dispersion by adsorption of hydrogen at high temperature. © 2004 Elsevier B.V. All rights reserved. Keywords: Ruthenium; Temperature-programmed desorption of hydrogen; Chemisorption; Adsorption kinetics; Hydrogen chemisorption; Metal–support interaction; Hydrogen spillover 1. Introduction The study of Fischer–Tropsch synthesis (FTS) has be- come an important technical and fundamental subject since Fischer and Tropsch first developed the process of produc- ing synthetic hydrocarbons in 1923 [1]. Although metal cat- alysts with high FTS activity such as iron, nickel and cobalt have used in commercial application, the group VIII metals transition metals have been reported as the good FTS catalyst with high activity and selectivity [2]. Ruthenium has been reported to be the most active and the most selective catalyst among the group VIII metals [2–4]. Recently, many works have been done on ruthenium-based catalysts which exhib- ited high hydrogenation selectivity in partial hydrogenation of benzene to cyclohexene [5,6]. To develop a more active and selective catalyst, it is important to understand the fac- tors affecting the reaction, such as the type of support; dis- persion of metal; the adsorption–desorption kinetics of the reactant gas, such as hydrogen, on the catalyst. The adsorption of hydrogen on group VIII metals has been extensively studied. Numerous studies have been devoted to ∗ Corresponding author. Fax: +886-3-425-2296. E-mail address: ywchen@cc.ncu.edu.tw (Y.-W. Chen). investigate the hydrogen adsorption phenomena over the sur- face of ruthenium single crystal by temperature-programmed desorption (TPD) [7], angle-resolved photoemission spec- troscopy [8] and low-energy electron diffraction (LEED) [7,9]. The dynamics of hydrogen adsorption/desorption on ruthenium single crystal indicated that there are two differ- ent binding states which were observed in work-function changes and well correlated with the two desorption peaks in TPD spectra between ruthenium and hydrogen [10,11]. However, the characteristics of hydrogen adsorption on metal–support systems would be different from that on the single crystals because of the metal–support interac- tions, which are affected by the factors including particle size, catalyst preparation, reduced temperature, etc. Bhatia et al. [12] have investigated the dynamics of hydrogen ad- sorption on silica-supported ruthenium catalysts by means of in situ NMR techniques. Two hydrogen-on-ruthenium peaks were observed at 300–473 K, the upfield NMR peak at ∼-60 ppm (-peak) observed at low pressures (P< 133 mbar) could be attributed to hydrogen dissociatively adsorbed on ruthenium particles; the second peak (-peak) occurring at ∼-30 ppm at pressures greater than 133 mbar represented weakly bound hydrogen. It has been reported [13] that hydrogen chemisorption is strongly suppressed on 0040-6031/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2004.03.007