Effect of manganese-based pigment catalyst on CO removal during biomass pyrolysis

A commercially available black pigment was evaluated for its potential as a CO oxidation catalyst during the pyrolysis of biomass. Characterization by X-ray diffraction (XRD) and scanning electron microscope (SEM) showed that the pigment consisted of a mixed oxide system (Cu_1.5Mn_1.5O₄–Mn₃O₄–Fe₂O₃) with an average particle size of 30–300 nm. The as received pigment catalyst was able to completely oxidize CO to CO₂ in a 4% CO–21% O₂–He gas mixture. In this study, the effect of catalyst on CO removal was evaluated during the pyrolysis of tobacco in inert and oxidizing conditions. The experiments were carried out in a flow tube reactor, which was connected to a multi-channel gas analyzer capable of measuring CO, CO₂ and O₂ concentrations. The catalyst was able to decrease the amount of CO production by 56% during the pyrolysis of biomass (tobacco) in the presence of oxygen (21% O₂–He). Oxidation of the biomass/catalyst mixture started at a lower temperature of 260 °C as opposed to a higher temperature of 300 °C in the absence of catalyst. Experiments in thermo gravimetric analyzer and differential scanning calorimeter (TG/DSC) mass spectrometer showed evidence of two-stage oxygen consumption during the pyrolysis of biomass/catalyst mixture while pure biomass pyrolized in single-stage oxygen consumption. Based on the experimental findings, a mechanism of reaction is proposed. The results show that the manganese-based mixed oxide pigment is a promising CO oxidation catalyst for biomass pyrolysis.