Evaluation of a spinel based pigment system as a CO oxidation catalyst

Commercially available black pigment consisting of mixed manganese, copper and iron oxides was tested as a catalyst as well as an oxidant for CO oxidation. The crystalline structures of the catalyst were determined by XRD as Cu1.5Mn1.5O4 mixed with Fe2O3 and Mn3O4 oxides. The fresh catalyst with 30-300 nm size and a BET surface area of 18.5 m2 g−1 was able to completely convert CO at 525 °C even at a significantly high COO2He gas flow rate of 1000 ml min−1 (corresponding space velocity being ∼310,000 h−1). While the reaction rate was independent of oxygen concentration in the range tested (0.8-9.9 vol.% of O2 at a constant CO concentration of 0.85%), it depended on CO concentration. The reaction order over fresh catalyst was measured to be 0.85 with respect to CO with an activation energy value of 47.9 kJ mol−1. Application of a reduction followed by oxidation type of heat treatment on fresh catalyst induced the formation of fine clusters or domains of ∼5 nm on the surface of the catalyst particles. This refined morphology with high density of defects led to a great improvement in catalytic activity. Complete CO conversion was achieved at 180 °C over a heat treated catalyst. This change in morphology also led to higher reducibility of mixed oxide system after heat treatment as indicated by TPR results. The mixed oxides of transition metals can be a viable alternative to precious metal and noble metal containing catalysts for oxidation of CO.