Catalytic activity of bifunctional transition metal oxide containing phosphated alumina catalysts in the dehydration of glycerol

A systematic study was conducted to evaluate the effect of different transition metal oxide loaded on phosphated alumina as catalysts for the gas-phase dehydration of glycerol. The series of MeO–Al2O3-PO4 catalysts at the constant Me:Al ratio was prepared by impregnation of alumina and characterized with respect to their textural properties, crystallinity, acidity and reducibility. Catalytic performance was tested at the constant operating conditions in the presence of steam. It was found that conversion, and acrolein formation increased with the increase of the total catalyst acidity; i.e., the selectivity to acrolein increased in the order: Ce < Mn < Cr < V ∼ Fe < Cu < Mo < W. The highest selectivity towards acrolein (54%) was observed over W contained catalyst after a long-term test, i.e., 30 h. For Ce, Fe and Cr catalysts low selectivity to acrolein (12–23%) was observed. Contrary CuOx–Al2O3-PO4 catalyst favored the formation of acetol (50%). In the case of Cr-, Mn- and V-containing alumina phosphates an enhanced formation of acetaldehyde and COx, was observed as a result of destructive glycerol cleavage. The V- and Fe-containing catalysts promote the formation of allyl alcohol. Finally, the change of the total acidity, oxidation state and crystallinity for spent catalysts was studied by NH3-TPD, TPO, TPR and XPS analysis. In general, MO–Al2O3-PO4 catalysts showed improved stability against deactivation which can be attributed to the oxidative properties of the transition metal oxide components that enhance coke removal.

The series of bifunctional aluminophosphates containing transition metal oxides were prepared, characterized and tested in the gas phase dehydration of glycerol. The product distribution depended on the redox properties of the particular metal component and the acidity of the catalyst. A change of the catalyst properties after reaction were investigated and discussed.Figure optionsDownload high-quality image (154 K)Download as PowerPoint slideHighlights
► The total acidity of the catalysts influences the performance.
► WOx and MoOx containing catalysts exhibit a high selectivity for acrolein.
► WOx, MoOx and CuO–Al2O3-PO4 catalysts are stable under reaction conditions.
► Transition metal oxides support a self regeneration of catalysts.