JOURNAL OF CATALYSIS 178, 84–93 (1998) ARTICLE NO. CA982129 Characterization of Supported Ruthenium Catalysts Derived from Reaction of Ru 3 (CO) 12 with Rare Earth Oxides Linda A. Bruce, Manh Hoang, 1 Anthony E. Hughes, and Terence W. Turney C.S.I.R.O Manufacturing Science and Technology, Private Bag 33, Clayton South MDC, Victoria, 3169, Australia Received September 4, 1997; revised April 13, 1998; accepted April 28, 1998 The surface chemistry of supported ruthenium on high surface area (>50 m 2 g −1 ) rare earth oxides (La, Ce, Pr, Tb, Ho, and Yb) has been studied by temperature-programmed reduction, temperature- programmed oxidation, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and hydrogen chemisorption. Re- duction of carbonyl ligands and surface carbonate by H 2 takes place in the range 255 ◦ C < T < 300 ◦ C, with evolution of CH 4 and forma- tion of nanometer-sized Ru particles. The Ru nanocrystallites were readily oxidized to RuO 2 , which strongly interacted with the sup- port. Prolonged heating (6 h) in 1% O 2 /He at 350 ◦ C led to loss of free RuO 2 from the support, but shorter term heating resulted in rearrangement of RuO 2 on the support, as revealed by alteration in the reduction profile with varying oxidation conditions. Hydro- gen adsorption–desorption experiments showed that dispersion of Ru metal was increased by the reduction–oxidation–reduction cycle for La and Yb but not the other oxides. Facile reduction of Ce, Pr, and Tb oxides was attributed to the dissociative chemisorption of H 2 on Ru metal nanocrystallites, and spillover of atomic species to the support. Reducible oxides such as CeO 2 and Pr 6 O 11 have been found to be effective support for the production of lower alkene from synthesis gas. c  1998 Academic Press Key Words: characterisation of supported ruthenium catalyst; supported ruthenium on rare earth oxides; Fischer–Tropsch syn- thesis. INTRODUCTION Numerous studies have been devoted to the influence of the support on the Ru catalyzed hydrogenation of CO (1–8). Support effects on catalyst performance can arise from al- teration of the electronic characteristics of the active metal, or through promotion or inhibition of secondary reactions on the support itself. Thus, a characteristic of acidic supports is a rich carbonium ion chemistry, leading to numerous sec- ondary reactions (e.g., chain branching, cracking, and hy- drogenation reactions). In contrast, such reactions on basic supports are minimal. A number of earlier studies have concentrated on MgO as a basic support for Ru-catalyzed CO hydrogenation, with 1 To whom correspondence should be addressed. very variable outcome as to the products (5–7). However, there are also studies on La 2 O 3 and CeO 2 , in which sub- stantial lower olefin production has been reported (4, 7), demonstrating the expected relative inhibition of secondary carbonium ion rearrangements on a basic support. In partic- ular, we have previously reported a high activity and stable Ru promoted Co/CeO 2 catalyst with good olefin selectivity and low CO 2 production (8). To better understand the per- formance of that Ru/Co/CeO 2 catalyst, we have undertaken a systematic study of the components and their interactions. Previous publications have reported our work on the syn- thesis of high area ceria and its surface and bulk properties as a function of area (9) and the interaction of Ru 3 (CO) 12 with rare earth oxides to form surface Ru carbonyl species (10). This publication describes the reduction of those sur- face carbonyl species, their properties, and Fischer–Tropsch activity with subsequent publications examining the influ- ence of CO 2 and H 2 O on the catalyst. A method for the preparation of rare earth oxides with high surface areas, between 50 and 200 m 2 g −1 , has been reported (11). These high surface area oxides introduce the possibility of designing catalysts which are likely to effect highly selective hydrogenation of carbon monoxide to un- branched lower olefins with minimal carbon dioxide for- mation. Thus, facile carbonation of the support by CO 2 , produced in the water–gas shift reaction, to form rare earth carbonate species, becomes a likely reaction. For the rare earths of variable oxidation state, Ce, Pr, and Tb, reduction of the high area surface or of the bulk support itself can occur by H 2 spillover. In a previous paper Fourier trans- form infrared (FTIR) spectroscopy and X-ray photoelec- tron spectroscopy (XPS) were used to identify the surface species [(OC) 2 Ru(OM) 2 ] n at 2 wt% Ru loading, and possi- bly [Ru 3 (μ-H)(CO) 10 (μ-OM)] at 5% metal loadings (10). The present paper investigates the reduction of these sur- face species on La 2 O 3 , Ho 2 O 3 , Yb 2 O 3 , CeO 2 , Pr 4 O 7 , Tb 4 O 7 , and their subsequent oxidation–reduction. EXPERIMENTAL Syntheses and characterization of high area M 2 O 3 (M = La, Ho, and Yb), CeO 2 , Pr 6 O 11 , and Tb 4 O 7 powders are 0021-9517/98 $25.00 Copyright c  1998 by Academic Press All rights of reproduction in any form reserved. 84