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 70.1 mol% can be achieved over the as-synthesized VPO catalyst using an aqueous glycerol solution (36.5 wt.%) feed and a liquid hourly space velocity (LHSV) of 4 h(-1) at 320 degrees C. Moreover, the derived VPO catalyst can handle heavy loading of reaction feed, such as a concentrated glycerol solution (50.0 wt%) or a notably high LHSV of 12 h(-1), and still retain reasonable acrolein yields (45-65 mol%), giving acrolein formation rate up to 35.3 mmol g(cat)(-1) h(-1). Techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and hydrogen temperature programmed reduction (H-2-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, V-O bonding strength, and Bronsted surface acidity. Balanced surface V5+/V4+ ratio and suitable density of medium strong acid sites are found to be critical to accomplish superior activity. (C) 2014 Elsevier B.V. All rights reserved.