Abstract: The metallic surface structure of supported Ru catalysts, activated at different pretreatment conditions, was investigated by following the development of IR bands due to adsorbed CO, as well as by following the methane formation in temperature-programmed surface reaction(TPSR-MS) of adsorbed CO in a H_2 flow. It revealed that there existed three kinds of active sites, designated as S_1, S_2 and S_3 sites, respectively. The S_1 sites, characterized by low frequency(LF) bands of 1980～2060 cm~(-1) for linearly adsorbed CO, were attributed to metallic Ru particles with almost no interaction with the support. The TPSR-MS results showed that, when reaction with H_2, the adsorbed CO on these sites changed into CH_4 at a lower temperature of ca. 450 K, varying with activated conditions. On the other hand, the S_2 sites were visualized to be interfacial Ru particles in direct contact with supporting materials, and exhibited stronger interaction with support. As a result of this MSI effect, the S_2 sites would result in the formation of electron-deficient Ru~(δ+) sites, and maintain high dispersive states of metal catalysts, and also adsorb CO with configuation of Ru~(δ+)-CO at 2075±5 cm~(-1) mediun frequency (MF_2). Upon hydrogenation, the adsorbed CO of formed methane at a much higher temperature of ca. 650 K. Obviously, the S_1 and S_2 sites are static sites of the conventional nature.
The interaction of CO with supported Ru catalysts led to the oxidative disruption of soluble surface Ru atoms or clusters with coordinatively unsaturation on the S_1 sites, as indicated by the slow transformation of the bands at 1980～2060 cm~(-1) due to Ru_x~0-CO to bands at 2135±5 cm (HF) and 2075±(MF_1) cm~(-1) attributed to surface-anchored carbonyl [(support-O)_2Ru(CO)_3]_n (n=1,2…) species, referred to as S_3 sites. The oxidative corrosive carbonylation of Ru is both favored ther-modynamically and feasible kinetically under our experimental conditions. It was demonstrated that at higher temperature, the presence of CO, especially with high partial pressure of hydrogen, such as in the case of TPSR-MS experiments, causes the reductive agglomeration of the S_3 sites, and the soluble Ru particles or clusters on the S_1 sites will be restored. These observation led us to postulate that the S_3 sites were active sites formed dynamically during the course of the Fischer-Tropsch reaction.

Key words: Ru catalyst, F-T synthesis, Active structure