Gas-phase dehydration of glycerol to acrolein over Al2O3-, SiO2-, and TiO2-supported Nb- and W-oxide catalysts

• Supported W- and Nb-oxides are active for dehydration of glycerol to form acrolein.
• Brønsted acid W and Nb sites are selective for acrolein formation.
• Deactivation of the catalyst occurs with time on stream.
• Addition of oxygen to the feed gives reduced deactivation rate.
• With oxygen, W-oxide on TiO2 gives 80% selectivity to acrolein at high conversion.

Hypothetical monolayer loadings of niobium and tungsten oxide supported on alumina, silica, and titania were investigated as catalysts for the dehydration of glycerol to produce acrolein. Besides activity measurements, to have information about the supported structures, the catalysts were characterized by XRD, Raman spectroscopy, XPS, XANES, and FTIR combined with adsorption of pyridine and CO2. Compared with silica showing the presence of crystalline Nb2O5 and WO3, alumina and titania gave better dispersion and formation of hydrated niobate and tungstate species. Deactivation of the catalysts occurred with time on stream. However, the stability was improved considerably by adding oxygen to the feed. A dependence of the selectivity to acrolein on the Brønsted acidity of the catalyst was observed. Under anaerobic conditions, an alumina-supported mixed Nb–W-oxide catalyst gave a selectivity of more than 70% for glycerol conversions above 40%. Even better selectivity was obtained using a catalyst with tungsten oxide supported on titania, which gave 80% selectivity under aerobic conditions at high conversion.

Brønsted acid sites on supported Nb- and W-oxides are active and selective for the dehydration of glycerol to form acrolein. Adding oxygen to the feed of glycerol and water improves the stability of the catalyst.Figure optionsDownload high-quality image (177 K)Download as PowerPoint slide