Dynamic Effects in CO Adsorption on Ru/ZSM-5. Part II: Thermal Stability and Reactivity of CO Adsorbed Species

Abstract

The stability and reactivity of CO species adsorbed on Ru/ZSM-5 have been studied by in situ diffuse reflectance infrared spectroscopy (DRIFT). Three species were detected: a linearly adsorbed CO (2045 ± 10 cm⁻¹) on metallic Ru and two multicarbonyl species (2138-2080 cm⁻¹ and 2150-2086 cm⁻¹) on oxidized Ru. The most strongly held species was the linearly adsorbed CO. Among the two multicarbonyl species, the one showing a doublet at 2150 and 2086 cm⁻¹ was more stable than the other. Because it is believed that the formation of the 2150-2086 cm⁻¹ and the 2138-2080 cm⁻¹ species involved silanol and Brønsted OH groups, respectively, it is inferred that the species with a low-frequency doublet (2138-2080) is predominantly located within the pore network of the HZSM-5 zeolite, while the other multicarbonyl species is mainly sited on the external surface of the zeolite. The latter species was found to be more stable than the other multicarbonyl species.

Keywords

CO adsorption Ruthenium ZSM-5 zeolite

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