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

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 (less than or similar to 1 mm), 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 (similar to 10 nm), which was able to completely oxidize toluene at similar to 240 degrees 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 AMn(2)O(4) and presents the advantage of easy catalyst forming. (C) 2012 Elsevier B. V. All rights reserved.