Selective Aerobic Oxidation of Furfural into Furoic Acid over a Highly Recyclable MnO2@CeO2 Core-Shell Oxide: The Role of the Morphology of the Catalyst

In this paper, we describe the use of a MnO2@CeO2 core-shell oxide in the furfural oxidation into furoic acid with molecular oxygen in water as solvent. MnO2 is the active oxidant species. The catalyst was prepared using two different synthetic procedures (high energy milling, HEM; or microwave-assisted hydrothermal, MWHT), and the activity of two samples was compared with that of commercial MnO2. MnO2@CeO2 MWHT exhibits excellent catalytic properties (conversion of furaldehyde >95% and selectivity into furoic acid equal to 100%) with almost no Mn-leaching over 10 cycles without significant loss of activity. Catalyst calcination temperature, furfural solution concentration, and reaction conditions were evaluated with respect to the furoic acid yield. The XPS, EDX, SEM, and acidic-basic properties of the catalysts were used to explain the different behavior of the catalytic materials. Both commercial and biosourced samples of furfural were used, showing that the presence of biocomponents in the real samples may affect the rate of oxidation, but not the selectivity of the catalyst.