TPR and FT-IR studies on carbonyl cluster derived Co-Ru/SiO₂ catalysts

The decomposition of the Co_4-nRu_nH_n(CO)_xSiO₂ (where n = 0–4 and x = 12 or 13) and (CO₄(CO)₁₂ + Ru₄H₄(CO)₁₂)/SiO₂ catalysts was studied by temperature-programmed reduction (TPR) and in-situ diffuse reflectance FT-IR techniques. The FT-IR studies suggested that Ru₄H₄(CO)₁₂, CoRu₃H₃(CO)₁₂ and Co₃RuH(CO)₁₂ clusters on silica were more stable in room temperature than Co₄(CO)₁₂, Co₂Ru₂H₂(CO)₁₂ and Co₂Ru₂(CO)₁₃ clusters. The FT-IR measurements also indicated that all precursors decomposed during thermal treatment, but the distinct temperature of decarbonylation was not necessarily noticeable. On the other hand, in TPR, the CO desorption peak maxima for the precursors were 123°C for (Co₄(CO)₁₂ + Ru₄H₄(CO)₁₂), 127°C for CoRu₃H₃(CO)₁₂, 133°C for Co₂Ru₂(CO)₁₃, 137°C for Co₄(CO)₁₂, 144°C for Co₂Ru₂H₂(CO)₁₂, 148°C for Co₃RuH(CO)₁₂ and 185°C for Ru₄H₄(CO)₁₂. Thus, the catalysts with 1:1 atomic ratio of Co:Ru decarbonylated at different temperatures. The temperature of decarbonylation was lower for Co₂Ru₂(CO)₁₃/SiO₂ than for Co₂Ru₂H₂(CO)₁₂/SiO₂, i.e., cobalt influenced the decarbonylation more in the first case. In accordance, the CO hydrogenation activity and selectivity results for the decarbonylated catalysts suggested that Co₂Ru₂(CO)₁₃/SiO₂ exhibited the characteristics of cobalt more than Co₂Ru₂H₂(CO)₁₂/SiO₂ did.