Multiphase reaction media involving water and carbon dioxide for selective hydrogenation

• Water and/or CO2 promote the selective hydrogenation.
• Water–organic and water–organic–solid interfaces control the product selectivity.
• Catalyst deactivation is suppressed by the presence of water and CO2.

The features of multiphase reaction media using water (bulk water, supported thin aqueous phase) and dense phase carbon dioxide are reviewed for selective hydrogenation of carbonyl, nitro, and cyano compounds. The interface of aqueous and organic phases is important in determining the rate of hydrogenation and the product selectivity. For supported aqueous phase catalysts, the interface between the thin aqueous film and a support material (for example, porous silica gel) has also an influential impact. The pressurization of a liquid reaction mixture (organic and/or aqueous phases) with carbon dioxide shows interesting positive effects on the reaction rate, the product selectivity, and the deactivation of a conventional supported metal catalyst. In some cases the use of both water and dense phase carbon dioxide serves as an effective reaction medium. In other words, these green solvents may act as reaction promoters. Possible roles of their actions are discussed.

Multiphase media involving water and dense phase CO2 are promising for selective hydrogenation reactions.Figure optionsDownload high-quality image (104 K)Download as PowerPoint slide