Partial hydrodeoxygenation of corn cob hydrolysate over palladium catalysts to produce 1-hydroxy-2-pentanone

Treatment of acidic corn cob hydrolysate under hydrodeoxygenation conditions gives 1-hydroxy-2-ketone as the primary product. [Display omitted] •Hydrolyzed corn cob is converted to hydroxy-2-pentanone.•Pd/Beta is stabilized with lanthanum against activity loss.•pH of reaction solution affects selectivity.•A low molecular weight hydrolignin is collected. Milled corn cobs were hydrolyzed with 50 mM H2SO4 resulting in a hydrolysate rich in solubilized pentose sugars and particulate aromatic oligomers from the hemicellulose portion of the corn cobs. Following centrifugation to remove the solids, the acidic supernatant was treated under hydrodeoxygenation conditions of 3.5–7 MPa H2 at 160 °C with supported Rh, Pt, and Pd catalysts. Supports examined were alumina, silica-alumina, and the zeolites ZSM-5 and Beta. All three metals supported on the zeolites were more effective in producing 1-hydroxy-2-pentanone (HPO) than they were when supported on the mesoporous aluminas. Ultimately, 2 wt% Pd/Beta was chosen for further study and development. The selectivity to HPO was 90% and the yield was 10–14% of the starting mass of cob. With repeated use of the catalyst, the selectivity was unchanged but the yield fell as decreased activity allowed pentose dehydration to furfural to increase. It was found that addition of La to the support decreased the loss of activity substantially. The catalysts were characterized by gas sorption analysis, powder XRD, XPS, STEM-EDS, and H2-TPR. The reaction mechanism was probed using 13C-xylose as substrate.