Niobium-modified hydrotalcite catalysts: Sustainable conversion of waste glycerol to valuable chemicals

[Display omitted] •Niobium-modified hydrotalcite prepared by ion exchange using peroxoniobate species.•Catalyst calcination produces a composite material (an MgAl mixed oxide and Nb2O5).•Catalytic tests performed in continuous-flow fixed bed reactor (PBR) on pilot-scale.•High glycerol conversion to valuable products like formic acid and diglycerol.•Nb increases the acidity of the MgAl catalyst and the diglycerol formation. Nb-modified MgAlmixed oxide catalysts were prepared by ion exchange using an MgAl hydrotalcite and peroxoniobate complex as precursors. After calcination, the Nb-MgAl revealed to be a composite material (MgAl mixed oxide with segregated Nb2O5 nanoparticles), with an increased specific surface area (229 m2 g−1) compared to bare MgAl (88 m2 g−1). XRD confirmed that part of the Nb atoms was inserted in the MgAl lattice thus causing the oxide doping. Furthermore, the Nb precursor favored the incorporation of a high amount of Nb in the catalyst (18 wt.%). Reactions performed in a continuous flow fixed-bed reactor (PBR) on a pilot scale showed that the MgAl and Nb-MgAl are quite active and stable catalysts for the conversion of the waste glycerol (> 90 %), as generated in the biodiesel industry. The valuable chemicals obtained (i.e., diglycerol, formic acid, and dioxane) demonstrates the potential industrial use of the catalysts presented in this work.