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Studying the adsorption of liquids on catalysts using Attenuated Total Reflection (ATR) spectroscopy

Attenuated total reflectance (ATR) is a technique that when used together with infrared spectroscopy enables liquids to be examined directly. In principle the liquid can be investigated under catalytic reaction conditions. A beam of infrared light is passed through the ATR crystal in such a way that it reflects multiple times off the internal surface in contact with the sample.

 

The penetration depth of the infrared beam into a sample is about 0.5 microns so by coating the surface of the ATR crystal with very finely divided catalyst powder it is possible to investigate liquids adsorbed on the surface of the catalyst.

 

To test the flow system with the ATR, D6-acetone was switched for normal acetone and the profiles recorded. The similarity in thw tow profiles shows that the system is well behaved:

 

In contrast when water and dioxane are switched,there are uneven profiles showing that dioxane flushes water from the cell much faster than water can flush dioxane from the cell:

 

In the hydrogenation reaction of benzylacetone, ATR can distinguish different solvent/solute interactions by measuring the position of the C=O vibration in the infared spectrum of the benzylacetone. These results are consistent with those obtained using NMR spectroscopy.

 

To monitor catalytic reactions by ATR it is necessary to be able to distiguish the various reactants and products. Preliminary experiments show that this is possible for the catalytic hydrogenation of benzylacetone: