Catalysis Letters 36 (1996) 41--49 41 Effects of ethylene glycol addition on the properties of Ru/A1203 catalyst prepared by sol-gel method J.C. Yang and Y.G. Shul Departmentof Chemical Engineering, YonseiUniversity, Sinchondong Sudaemungu, 120-749,Seoul, Korea Received16June 1995;accepted 31 August 1995 Ru/A1203 catalysts were prepared by sol-gel method with an organic additive (ethyleneglycol). The effect of the addition of ethyleneglycolon the properties of Ru/A1203 was characterized by BET,XRD, EXAFS, and TGA/DTA. Ethyleneglycol was effectiveto promote the phase transition of a-A1203 even at 800~ calcination with high surface area. This finding is ascribed to the modified structure of aluminum alkoxideby ethyleneglycoladdition in the solution state. Ethyleneglycolis also effective to get small particles of ruthenium after the reduction at 500~ The EXAFS and UV-Vis spectra of Ru complex revealed that the coordination structure of Ru depended on the additive used. The ethyleneglycolsol prefers to form octahedral Ru complex. This Ru complexin alumina matrix is stable up to 200~ and forms small Ru oxideparticles even at 300~ calcination. This sug- gests that ethylene glycolcoordinates to the Ru complex as well as to aluminum ion in the initial state, whichis important to con- trol the final properties of the Ru/A1203 catalyst. Keywords: sol-gel; Ru/AI203; ethylene glycol; characterization; chelatingagent 1. Introduction Ruthenium supported catalysts have been widely used in Fischer-Tropsch synthesis [1], hydrogenolysis of paraffins and olefins [2]. In these reactions, catalytic activity and selectivity to products are greatly affected by the dispersion of Ru and the nature of support such as surface area, pore structure and thermal stability [3]. It is well-known that the dispersion and nature of support are strongly dependent on the method of catalyst prepa- ration employed [4]. Recently, the sol-gel method that starts from homo- geneous alkoxide solution has been proposed. The sol- gel method starts with the molecular precursor of the support material and active metal. A greater degree of control over the catalyst preparation can be achieved in comparison to the traditional preparation method [5]. The advantages of the sol-gel method compared with the conventional impregnation method are as follows: (a) homogeneity and high purity, (b) high BET surface area and well-defined pore control and (c) easy control of active metal particle size. Lopez et al. prepared Ru/ SiO2 catalyst by the sol-gel method, whereby most of ruthenium particles were incorporated in the silica matrix. This catalyst allows better selectivity and greater resistance to coke formation and deactivation in benzene hydrogenation reaction than the catalyst prepared by the traditional impregnation method, which is attributed to structural differences in the prepared catalysts [6-9]. Balakrishman obtained very porous and well- dispersed Pt/A1203 by controlling the preparation parameters like H20/alkoxide ratio in sol-gel prepara- tion [ 10]. The chemical modification of metal alkoxides with chelating agents such as beta-diketones is known to be very effective for the control of reactivities and conden- sation process of metal alkoxides [11]. The structural modification of A1 alkoxide by ethylacetoacetate has been reported to yield very fine and porous AIEO3 [12]. ~ Inoui et al. prepared the bohemite in which ethylene gly- col moiety was incorporated between alumina layers through covalent bonding by thermal decomposition of aluminum isopropoxide in inert organic solvent at 250- 300~ [13,14]. Mizukami et al. investigated the effects of organic additives on the AlEO3 gel by sol-gel method, and the thermal stability and pore structure of the pre- pared AlaO3 appeared to be greatly affected by the com- plexing ability of the organic solvent [15]. Shul et al. found hexylene glycol was an effective organic additive to lower the phase transition temperature of rutile from the alkoxide derived TiO2 gel in oxygen steam treatment at 300~ [16]. These studies denote the importance of chelating agents which affect the thermal stability and morphology of prepared gel in sol-gel transformation. In this study, the effects of ethylene glycol addition on the properties of Ru/AlEO3 catalysts were discussed. The changes of coordination state around Ru, from initial solution to final reduced metal state, were charac- terized by means of BET, XRD, TGA/DTA, 13C- NMR, and EXAFS. 2. Experimental 2.1. Preparation of 5 wt% Ru/AI203 catalyst The schematic preparation procedure of Ru/A1203 by the sol-gel method was as follows (fig. 1): 12.3 g of 9 J.C. Baltzer AG, Science Publishers