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

Abstract

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 35.3mmolgcat−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.