The role of Lewis and Br�nsted site in the dehydration of glycerol on niobium oxide and Na+-exchanged niobium oxide was investigated using FTIR spectroscopy supported by DFT calculations. Glycerol was impregnated on the catalysts at room temperature using an ex-situ method. Under high vacuum condition, glycerol forms a stable multidentate alkoxy species through its primary hydroxyl groups with the Lewis sites consisting of coordinatively unsaturated Nb atoms. In addition, dehydration products such as hydroxyacetone and acrolein were observed on niobium oxide at room temperature. When more than a monolayer of glycerol was impregnated, monoaromatic compounds were formed on the surface upon heating. On Na+-exchange niobium oxide where Br�nsted sites were blocked, only hydroxyacetone was observed as a dehydration product. Other surface species such as acrolein and aromatic compounds were not present. This demonstrates that Lewis sites are responsible for the dehydration of glycerol on its primary hydroxyl group, forming hydroxyacetone. Br�nsted sites are needed to remove the secondary hydroxyl group in the initial dehydration step, followed by dehydration on a primary hydroxyl group by a Lewis site to form acrolein. Br�nsted sites are also involved in the formation of aromatic compounds, which eventually form coke and deactivate the catalyst.

Role of Lewis and Br�nsted site in the dehydration of glycerol over niobia

247th National Meeting (2014)

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