CO hydrogenation catalysts prepared from molecular ruthenium carbonyl clusters: Effects of the support on catalyst structure and stability

Abstract

Ruthenium catalysts supported on SiO 2, TiO 2, γ-Al 2O 3, and MgO were prepared from organic solutions of metal carbonyl clusters ([Ru 3(CO) 12], [H 4Ru 4(CO) 12], and [H 2Ru 6(CO) 18]). The activities, selectivities, and stabilities of the catalysts were measured for CO hydrogenation at 275 °C and 10 and 70 atm. Fresh and used catalysts were characterized by infrared, ultraviolet, and X-ray fluorescence spectroscopies and electron microscopy. Catalyst performance depended strongly on the support. The molecular metal cluster precursors on SiO 2 were only weakly bound, and the ruthenium species formed at reaction temperature were converted into volatile ruthenium carbonyls and lost from the catalyst. The ruthenium clusters on TiO 2 and γ-Al 2O 3 were converted into highly dispersed particles of metal, and consequently these catalysts were comparable to conventionally prepared catalysts, being relatively active and stable. In contrast, the ruthenium carbonyls on the basic MgO surface were converted into molecular cluster anions, [Ru 6C(CO) 16] 2−, which are stable but have little if any catalytic activity.