New synthesis of nanosized Cu–Mn spinels as efficient oxidation catalysts

[Display omitted] ► Copper manganese oxides Cu1.5Mn1.5O4, Mn3O4, CuO are prepared from ionotropic alginate gel. ► Alginate precursor as biopolymer auxiliary provides nanoscale oxide dispersion. ► Cubic spinel Cu1.5Mn1.5O4 nanoparticles completely oxidize toluene at ∼240°C. ► Ionotropic alginate gel used as potential precursor for manganite spinels AMn2O4. Copper manganese nanoscale oxides were prepared using a novel method with low cost natural biopolymer precursor, alginate, and their catalytic activity was evaluated for the complete oxidation of toluene as a model VOC. Depending on the Cu/Mn ratio the following oxides were formed: Mn3O4, Cu1.5Mn1.5O4, CuO or a mixture of these phases, as detected by XRD. The nanocrystals aggregate in small spheres (≲1mm), which retain the shape of the parent gel and present homogeneous composition as characterized by TEM and SEM-EDX. The best performance for toluene combustion was observed for the cubic spinel Cu1.5Mn1.5O4 nanoparticles (∼10nm), which was able to completely oxidize toluene at ∼240°C. For the pure oxides the activity order: Cu1.5Mn1.5O4>Mn3O4>CuO, correlates with the TPR results as the catalyst with the higher redox potential shows higher activity. For comparison the TiO2 supported oxides were also studied and alginate issued Cu1.5Mn1.5O4 mixed with TiO2 presented similar activity as the Cu–Mn oxide deposited on TiO2 by incipient wetness impregnation however the overall activity of supported oxides was lower than for the unsupported Cu1.5Mn1.5O4. The method used for the synthesis of copper manganite has great potential as it can be extended to other manganite spinels of general formula AMn2O4 and presents the advantage of easy catalyst forming.