JOURNAL OF CATALYSIS 158, 427–438 (1996) ARTICLE NO. 0044 Studies on the Sulfur Poisoning of Ru–RuO x /TiO 2 Catalyst for the Adsorption and Methanation of Carbon Monoxide V. S. Kamble,* V. P. Londhe,* N. M. Gupta, 1, * K. Ravindranathan Thampi,† and M. Gra ¨ tzel† *Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay-400 085, India; and †Department of Chemistry, Swiss Federal Institute of Technology, Lausanne, CH 1015, Switzerland Received November 8, 1994; revised September 13, 1995 Ru/TiO 2 catalyst to a flow of CO or CO + H 2 gave rise The effects of sulfur poisoning on the chemisorption and on to several CO binding states involving ruthenium sites of the methanation of carbon monoxide over Ru/TiO 2 catalyst different oxidation states. These species were identified were investigated by FTIR spectroscopy and volumetric gas with the CO held in various multicarbonyl and linear- adsorption measurements. The CS 2 molecules are  bonded bonded monocarbonyl forms. With a rise in the catalyst to Ru sites through one of the sulfur atoms and decompose to temperature, the multicarbonyl species transformed pro- the constituent elements on thermal activation. Each S atom gressively to monocarbonyls and at temperatures above may deactivate 3 to 10 metal sites even at low coverages, the 420 K, the formation of methylene group-containing hy- effect being more pronounced on the chemisorption of hydro- drocarbon chains was observed. The methylene groups gen. The deposited sulfur (and possibly carbon also) sterically gave way to methane formation when the catalyst tempera- hinders the formation of certain multicarbonyl and monocarbo- ture was raised further. It was therefore of interest to nyl species (CO in 2055–2140 cm 1 region), which otherwise learn how these individual steps would be affected by the transform to methane via surface methylene groups in the presence of chemisorbed hydrogen and are found to play an presence of a sulfur compound such as CS 2 in the reacting important role in the low-temperature methanation activity of stream. The present Fourier-transform infrared spectro- the studied catalyst. The Ru–CO species giving rise to lower- scopic study was carried out to investigate the nature of frequency vibrational bands are affected to a lesser extent. The surface species formed during exposure of a Ru/TiO 2 cata- presence of sulfur also results in the development of some new lyst to the doses of CS 2 and then to CO + H 2 at different CO binding states which are weak and are identified with the temperatures under static mode conditions. The effect of CO and S coadsorbed at Ru sites of different oxidation states evacuation in between two exposures and the effect of or of varying crystallographic nature. The CO adsorbed in these preadsorbed CO + H 2 on the subsequent adsorption of states is not reactive to hydrogen.  1996 Academic Press, Inc. CS 2 molecules were also evaluated. Corresponding experi- ments were performed using metal-free titania to assess the possible role of support in the catalyst poisoning. The INTRODUCTION effect of preadsorbed sulfur on the H 2 and CO adsorption over Ru/TiO 2 was evaluated by volumetric methods. The trace amount of sulfur in reacting streams is known to poison Group VIII metal catalysts for different adsorption/hydrogenation reactions (1–5) even though EXPERIMENTAL some relatively S-resistant noble metal catalysts have also been reported (6). Various issues, such as the mode of Catalyst. The preparation method and the characteris- adsorption of a sulfur compound on the catalyst surface tics of a Ru–RuO x /TiO 2 catalyst used in this study have or its support and the role it plays in the catalytic poisoning, been reported earlier (8–10). The catalyst contained about are, however, not yet well resolved. As compared to the 3.8 wt% of ruthenium with a metal dispersion of about studies reported on Ni and Pt metals, only scarce literature 55% and had a N 2 absorption BET area of about 50 m 2 is presently available on the S poisoning of Ru metal, g -1 . About 25% of ruthenium existed in the oxide form particularly when dispersed on an oxide support. We have and the metal particle size ranged between 10 and 30 A ˚ . reported earlier (7) that the exposure of a partially oxidized FTIR spectroscopy. The infrared spectra were re- corded in transmittance mode using a high-pressure, high- temperature stainless-steel cell described earlier in detail 1 To whom correspondence should be addressed. E-mail: nmgupta@- magnum.barct1.ernet.in (7). The cell had a provision of heating a catalyst wafer in 427 0021-9517/96 $12.00 Copyright  1996 by Academic Press, Inc. All rights of reproduction in any form reserved.