Equilibrium ruthenium catalysis

To accelerate the approach to equilibrium, the oxide catalysis employed are based on Group 7 metals, exclusively iron in practice (Fe,0 i. A number of promoters help to improve performance, including Al202 which increases the active surface area of the particles, and K20. SiO,. MeO. CaO etc, which improve stability, and increase activity and resistance to poisoning. Systems currently under development make use of ruthenium... 

A key function of the ruthenium promoter (and other promoter species) is to moderate the iodide concentration. In situ HPIR spectroscopy showed that under catalytic conditions, the ruthenium promoter exists mainly as [RulCOlala] , in equilibrium with smaller amounts of [Ru(CO)3l2(sol)] and [Ru(GO)2l2(sol)2]. The presence of a high concentration of [Ru(CO)3l3] H30 increases the Brpnsted acidity, and is thought to accelerate the reaction of methyl acetate with HI by acid catalysis. Consistent with this, the exchange of isotopically labeled methyl groups between Mel and MeOAc is catalyzed by [Ru(C0)3l3] H30. " The promoter therefore acts not just as an iodide abstractor, but is able to promote recycling of ionic iodide back into methyl iodide, as indicated by the green cycle in Scheme 9. 

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