Vanadium pyrophosphate oxides: The role of preparation chemistry in determining renewable acrolein production from glycerol dehydration

Efficient acrolein production through selective dehydration of biomass-derivable glycerol was investigated over the vanadium pyrophosphate oxide (VPO) catalysts. Employing polyethylene glycol (PEG) additive in the preparation media and activating the VPO precursors in the butane-air atmosphere considerably enhanced catalyst performance for the target reaction. An acrolein yield of 70.1mol% can be achieved over the as-synthesized VPO catalyst using an aqueous glycerol solution (36.5wt.%) feed and a liquid hourly space velocity (LHSV) of 4h^-1 at 320°C. Moreover, the derived VPO catalyst can handle heavy loading of reaction feed, such as a concentrated glycerol solution (50.0wt%) or a notably high LHSV of 12h^-1, and still retain reasonable acrolein yields (45-65mol%), giving acrolein formation rate up to 35.3mmolg_cat^-1h^-1. Techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and hydrogen temperature programmed reduction (H₂-TPR) were employed to explore the nature of catalysts. Type of alcohol and addition of PEG adopted in catalyst preparation showed significant impact on sample crystallinity/morphology, surface V⁵⁺/V⁴⁺ ratio, VO bonding strength, and Brønsted surface acidity. Balanced surface V⁵⁺/V⁴⁺ ratio and suitable density of medium strong acid sites are found to be critical to accomplish superior activity.